Page 1 Exercise - 1B 1. Using prime factorization, find the HCF and LCM of (i) 36, 84 (ii) 23, 31 (iii)96, 404 (iv)144, 198 (v) 396, 1080 (vi)1152, 1664 In each case verify that HCF × LCM = product of given numbers. Sol: (i) Prime factorization: 36 = 2 2 × 3 84 = 2 2 × 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 = 12 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 7 = 252 (ii) Prime factorization: 23 = 23 31 = 31 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 23 × 31 = 713 (iii) Prime factorization: 96 = 2 5 × 3 404 = 2 2 × 101 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 5 × 3 × 101 = 9696 (iv)Prime factorization: Page 2 Exercise - 1B 1. Using prime factorization, find the HCF and LCM of (i) 36, 84 (ii) 23, 31 (iii)96, 404 (iv)144, 198 (v) 396, 1080 (vi)1152, 1664 In each case verify that HCF × LCM = product of given numbers. Sol: (i) Prime factorization: 36 = 2 2 × 3 84 = 2 2 × 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 = 12 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 7 = 252 (ii) Prime factorization: 23 = 23 31 = 31 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 23 × 31 = 713 (iii) Prime factorization: 96 = 2 5 × 3 404 = 2 2 × 101 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 5 × 3 × 101 = 9696 (iv)Prime factorization: 144 = 2 4 × 3 2 198 = 2 × 3 2 × 11 HCF = product of smallest power of each common prime factor in the numbers = 2 × 3 2 = 18 LCM = product of greatest power of each prime factor involved in the numbers = 2 4 × 3 2 × 11 = 1584 (v) Prime factorization: 396 = 2 2 × 3 2 × 11 1080 = 2 3 × 3 3 × 5 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 2 = 36 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 3 × 5 × 11 = 11880 (vi) Prime factorization: 1152 = 2 7 × 3 2 1664 = 2 7 × 13 HCF = product of smallest power of each common prime factor in the numbers = 2 7 = 128 LCM = product of greatest power of each prime factor involved in the numbers = 2 7 × 3 2 × 13 = 14976 2. Using prime factorization, find the HCF and LCM of (i) 8, 9, 25 (ii) 12,15, 21 (iii) 17,23,29 (iv) 24, 36, 40 (v) 30, 72, 432 (vi) 21, 28, 36, 45 Sol: (i) 8 = 2 × 2 × 2 = 2 3 9 = 3 × 3 = 3 2 25 = 5 × 5 = 5 2 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 2 × 5 2 = 1800 (ii) 12 = 2 × 2 × 3 = 2 2 × 3 15 = 3 × 5 21 = 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 3 LCM = product of greatest power of each prime factor involved in the numbers Page 3 Exercise - 1B 1. Using prime factorization, find the HCF and LCM of (i) 36, 84 (ii) 23, 31 (iii)96, 404 (iv)144, 198 (v) 396, 1080 (vi)1152, 1664 In each case verify that HCF × LCM = product of given numbers. Sol: (i) Prime factorization: 36 = 2 2 × 3 84 = 2 2 × 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 = 12 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 7 = 252 (ii) Prime factorization: 23 = 23 31 = 31 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 23 × 31 = 713 (iii) Prime factorization: 96 = 2 5 × 3 404 = 2 2 × 101 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 5 × 3 × 101 = 9696 (iv)Prime factorization: 144 = 2 4 × 3 2 198 = 2 × 3 2 × 11 HCF = product of smallest power of each common prime factor in the numbers = 2 × 3 2 = 18 LCM = product of greatest power of each prime factor involved in the numbers = 2 4 × 3 2 × 11 = 1584 (v) Prime factorization: 396 = 2 2 × 3 2 × 11 1080 = 2 3 × 3 3 × 5 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 2 = 36 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 3 × 5 × 11 = 11880 (vi) Prime factorization: 1152 = 2 7 × 3 2 1664 = 2 7 × 13 HCF = product of smallest power of each common prime factor in the numbers = 2 7 = 128 LCM = product of greatest power of each prime factor involved in the numbers = 2 7 × 3 2 × 13 = 14976 2. Using prime factorization, find the HCF and LCM of (i) 8, 9, 25 (ii) 12,15, 21 (iii) 17,23,29 (iv) 24, 36, 40 (v) 30, 72, 432 (vi) 21, 28, 36, 45 Sol: (i) 8 = 2 × 2 × 2 = 2 3 9 = 3 × 3 = 3 2 25 = 5 × 5 = 5 2 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 2 × 5 2 = 1800 (ii) 12 = 2 × 2 × 3 = 2 2 × 3 15 = 3 × 5 21 = 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 3 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 × 5 × 7 = 420 (iii) 17 = 17 23 = 23 29 = 29 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 17 × 23 × 29 = 11339 (iv) 24 = 2 × 2 × 2 × 3 = 2 3 × 3 36 = 2 × 2 × 3 × 3 = 2 2 × 3 2 40 = 2 × 2 × 2 × 5 = 2 3 × 5 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 2 × 5 = 360 (v) 30 = 2 × 3 × 5 72 = 2 × 2 × 2 × 3 × 3 = 2 3 × 3 2 432 = 2 × 2 × 2 × 2 × 3 × 3 × 3 = 2 4 × 3 3 HCF = product of smallest power of each common prime factor in the numbers = 2 × 3 = 6 LCM = product of greatest power of each prime factor involved in the numbers = 2 4 × 3 3 × 5 = 2160 (vi) 21 = 3 × 7 28 = 2 × 2 × 7 = 2 2 × 7 36 = 2 × 2 × 3 × 3 = 2 2 × 3 2 45 = 5 × 3 × 3 = 5 × 3 2 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 5 × 7 = 1260 3. The HCF of two numbers is 23 and their LCM is 1449. If one of the numbers is 161, find the other. Sol: Let the two numbers be a and b. Let the value of a be 161. Given: HCF = 23 and LCM = 1449 We know, a × b = HCF × LCM 161 × b = 23 × 1449 b = = = 207 Hence, the other number b is 207. Page 4 Exercise - 1B 1. Using prime factorization, find the HCF and LCM of (i) 36, 84 (ii) 23, 31 (iii)96, 404 (iv)144, 198 (v) 396, 1080 (vi)1152, 1664 In each case verify that HCF × LCM = product of given numbers. Sol: (i) Prime factorization: 36 = 2 2 × 3 84 = 2 2 × 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 = 12 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 7 = 252 (ii) Prime factorization: 23 = 23 31 = 31 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 23 × 31 = 713 (iii) Prime factorization: 96 = 2 5 × 3 404 = 2 2 × 101 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 5 × 3 × 101 = 9696 (iv)Prime factorization: 144 = 2 4 × 3 2 198 = 2 × 3 2 × 11 HCF = product of smallest power of each common prime factor in the numbers = 2 × 3 2 = 18 LCM = product of greatest power of each prime factor involved in the numbers = 2 4 × 3 2 × 11 = 1584 (v) Prime factorization: 396 = 2 2 × 3 2 × 11 1080 = 2 3 × 3 3 × 5 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 2 = 36 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 3 × 5 × 11 = 11880 (vi) Prime factorization: 1152 = 2 7 × 3 2 1664 = 2 7 × 13 HCF = product of smallest power of each common prime factor in the numbers = 2 7 = 128 LCM = product of greatest power of each prime factor involved in the numbers = 2 7 × 3 2 × 13 = 14976 2. Using prime factorization, find the HCF and LCM of (i) 8, 9, 25 (ii) 12,15, 21 (iii) 17,23,29 (iv) 24, 36, 40 (v) 30, 72, 432 (vi) 21, 28, 36, 45 Sol: (i) 8 = 2 × 2 × 2 = 2 3 9 = 3 × 3 = 3 2 25 = 5 × 5 = 5 2 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 2 × 5 2 = 1800 (ii) 12 = 2 × 2 × 3 = 2 2 × 3 15 = 3 × 5 21 = 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 3 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 × 5 × 7 = 420 (iii) 17 = 17 23 = 23 29 = 29 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 17 × 23 × 29 = 11339 (iv) 24 = 2 × 2 × 2 × 3 = 2 3 × 3 36 = 2 × 2 × 3 × 3 = 2 2 × 3 2 40 = 2 × 2 × 2 × 5 = 2 3 × 5 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 2 × 5 = 360 (v) 30 = 2 × 3 × 5 72 = 2 × 2 × 2 × 3 × 3 = 2 3 × 3 2 432 = 2 × 2 × 2 × 2 × 3 × 3 × 3 = 2 4 × 3 3 HCF = product of smallest power of each common prime factor in the numbers = 2 × 3 = 6 LCM = product of greatest power of each prime factor involved in the numbers = 2 4 × 3 3 × 5 = 2160 (vi) 21 = 3 × 7 28 = 2 × 2 × 7 = 2 2 × 7 36 = 2 × 2 × 3 × 3 = 2 2 × 3 2 45 = 5 × 3 × 3 = 5 × 3 2 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 5 × 7 = 1260 3. The HCF of two numbers is 23 and their LCM is 1449. If one of the numbers is 161, find the other. Sol: Let the two numbers be a and b. Let the value of a be 161. Given: HCF = 23 and LCM = 1449 We know, a × b = HCF × LCM 161 × b = 23 × 1449 b = = = 207 Hence, the other number b is 207. 4. The HCF of two numbers is 145 and their LCM is 2175. If one of the numbers is 725, find the other. Sol: HCF of two numbers = 145 LCM of two numbers = 2175 Let one of the two numbers be 725 and other be x . Using the formula, product of two numbers = HCF × LCM we conclude that 725 × x = 145 × 2175 x = = 435 Hence, the other number is 435. 5. The HCF of two numbers is 18 and their product is 12960. Find their LCM. Sol: HCF of two numbers = 18 Product of two numbers = 12960 Let their LCM be x . Using the formula, product of two numbers = HCF × LCM we conclude that 12960 = 18 × x x = = 720 Hence, their LCM is 720. 6. Is it possible to have two numbers whose HCF is 18 and LCM is 760? Give reason. Sol: No, it is not possible to have two numbers whose HCF is 18 and LCM is 760. Since, HCF must be a factor of LCM, but 18 is not factor of 760. 7. Find the simplest form of (i) 69 92 (ii) 473 645 (iii) 1095 1168 (iv) 368 496 Sol: (i) Prime factorization of 69 and 92 is: 69 = 3 × 23 92 = 2 2 × 23 Therefore, = = = Page 5 Exercise - 1B 1. Using prime factorization, find the HCF and LCM of (i) 36, 84 (ii) 23, 31 (iii)96, 404 (iv)144, 198 (v) 396, 1080 (vi)1152, 1664 In each case verify that HCF × LCM = product of given numbers. Sol: (i) Prime factorization: 36 = 2 2 × 3 84 = 2 2 × 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 = 12 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 7 = 252 (ii) Prime factorization: 23 = 23 31 = 31 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 23 × 31 = 713 (iii) Prime factorization: 96 = 2 5 × 3 404 = 2 2 × 101 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 5 × 3 × 101 = 9696 (iv)Prime factorization: 144 = 2 4 × 3 2 198 = 2 × 3 2 × 11 HCF = product of smallest power of each common prime factor in the numbers = 2 × 3 2 = 18 LCM = product of greatest power of each prime factor involved in the numbers = 2 4 × 3 2 × 11 = 1584 (v) Prime factorization: 396 = 2 2 × 3 2 × 11 1080 = 2 3 × 3 3 × 5 HCF = product of smallest power of each common prime factor in the numbers = 2 2 × 3 2 = 36 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 3 × 5 × 11 = 11880 (vi) Prime factorization: 1152 = 2 7 × 3 2 1664 = 2 7 × 13 HCF = product of smallest power of each common prime factor in the numbers = 2 7 = 128 LCM = product of greatest power of each prime factor involved in the numbers = 2 7 × 3 2 × 13 = 14976 2. Using prime factorization, find the HCF and LCM of (i) 8, 9, 25 (ii) 12,15, 21 (iii) 17,23,29 (iv) 24, 36, 40 (v) 30, 72, 432 (vi) 21, 28, 36, 45 Sol: (i) 8 = 2 × 2 × 2 = 2 3 9 = 3 × 3 = 3 2 25 = 5 × 5 = 5 2 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 2 × 5 2 = 1800 (ii) 12 = 2 × 2 × 3 = 2 2 × 3 15 = 3 × 5 21 = 3 × 7 HCF = product of smallest power of each common prime factor in the numbers = 3 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 × 5 × 7 = 420 (iii) 17 = 17 23 = 23 29 = 29 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 17 × 23 × 29 = 11339 (iv) 24 = 2 × 2 × 2 × 3 = 2 3 × 3 36 = 2 × 2 × 3 × 3 = 2 2 × 3 2 40 = 2 × 2 × 2 × 5 = 2 3 × 5 HCF = product of smallest power of each common prime factor in the numbers = 2 2 = 4 LCM = product of greatest power of each prime factor involved in the numbers = 2 3 × 3 2 × 5 = 360 (v) 30 = 2 × 3 × 5 72 = 2 × 2 × 2 × 3 × 3 = 2 3 × 3 2 432 = 2 × 2 × 2 × 2 × 3 × 3 × 3 = 2 4 × 3 3 HCF = product of smallest power of each common prime factor in the numbers = 2 × 3 = 6 LCM = product of greatest power of each prime factor involved in the numbers = 2 4 × 3 3 × 5 = 2160 (vi) 21 = 3 × 7 28 = 2 × 2 × 7 = 2 2 × 7 36 = 2 × 2 × 3 × 3 = 2 2 × 3 2 45 = 5 × 3 × 3 = 5 × 3 2 HCF = product of smallest power of each common prime factor in the numbers = 1 LCM = product of greatest power of each prime factor involved in the numbers = 2 2 × 3 2 × 5 × 7 = 1260 3. The HCF of two numbers is 23 and their LCM is 1449. If one of the numbers is 161, find the other. Sol: Let the two numbers be a and b. Let the value of a be 161. Given: HCF = 23 and LCM = 1449 We know, a × b = HCF × LCM 161 × b = 23 × 1449 b = = = 207 Hence, the other number b is 207. 4. The HCF of two numbers is 145 and their LCM is 2175. If one of the numbers is 725, find the other. Sol: HCF of two numbers = 145 LCM of two numbers = 2175 Let one of the two numbers be 725 and other be x . Using the formula, product of two numbers = HCF × LCM we conclude that 725 × x = 145 × 2175 x = = 435 Hence, the other number is 435. 5. The HCF of two numbers is 18 and their product is 12960. Find their LCM. Sol: HCF of two numbers = 18 Product of two numbers = 12960 Let their LCM be x . Using the formula, product of two numbers = HCF × LCM we conclude that 12960 = 18 × x x = = 720 Hence, their LCM is 720. 6. Is it possible to have two numbers whose HCF is 18 and LCM is 760? Give reason. Sol: No, it is not possible to have two numbers whose HCF is 18 and LCM is 760. Since, HCF must be a factor of LCM, but 18 is not factor of 760. 7. Find the simplest form of (i) 69 92 (ii) 473 645 (iii) 1095 1168 (iv) 368 496 Sol: (i) Prime factorization of 69 and 92 is: 69 = 3 × 23 92 = 2 2 × 23 Therefore, = = = Thus, simplest form of is . (ii) Prime factorization of 473 and 645 is: 473 = 11 × 43 645 = 3 × 5 × 43 Therefore, = = Thus, simplest form of is . (iii) Prime factorization of 1095 and 1168 is: 1095 = 3 × 5 × 73 1168 = 2 4 × 73 Therefore, = = Thus, simplest form of is . (iv) Prime factorization of 368 and 496 is: 368 = 2 4 × 23 496 = 2 4 × 31 Therefore, = = Thus, simplest form of is . 8. Find the largest number which divides 438 and 606 leaving remainder 6 in each case. Answer: Largest number which divides 438 and 606, leaving remainder 6 is actually the largest number which divides 438 6 = 432 and 606 6 = 600, leaving remainder 0. Therefore, HCF of 432 and 600 gives the largest number. Now, prime factors of 432 and 600 are: 432 = 2 4 × 3 3 600 = 2 3 × 3 × 5 2 HCF = product of smallest power of each common prime factor in the numbers = 2 3 × 3 = 24 Thus, the largest number which divides 438 and 606, leaving remainder 6 is 24. 9. Find the largest number which divides 320 and 457 leaving remainders 5 and 7 respectively. Answer: We know that the required number divides 315 (320 5) and 450 (457 7). Required number = HCF (315, 450)Read More

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