Page 1 Cbse-spot.blogspot.com 1 Class IX Chapter 15 – Probability Maths Exercise 15.1 Question 1: In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays. Find the probability that she did not hit a boundary. Answer: Number of times the batswoman hits a boundary = 6 Total number of balls played = 30 Number of times that the batswoman does not hit a boundary = 30 - 6 = 24 Question 2: 1500 families with 2 children were selected randomly, and the following data were recorded: Number of girls in a family 2 1 0 Number of families 475 814 211 Compute the probability of a family, chosen at random, having (i) 2 girls (ii) 1 girl (iii) No girl Also check whether the sum of these probabilities is 1. Page 2 Cbse-spot.blogspot.com 1 Class IX Chapter 15 – Probability Maths Exercise 15.1 Question 1: In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays. Find the probability that she did not hit a boundary. Answer: Number of times the batswoman hits a boundary = 6 Total number of balls played = 30 Number of times that the batswoman does not hit a boundary = 30 - 6 = 24 Question 2: 1500 families with 2 children were selected randomly, and the following data were recorded: Number of girls in a family 2 1 0 Number of families 475 814 211 Compute the probability of a family, chosen at random, having (i) 2 girls (ii) 1 girl (iii) No girl Also check whether the sum of these probabilities is 1. Cbse-spot.blogspot.com 2 Answer: Total number of families = 475 + 814 + 211 = 1500 (i) Number of families having 2 girls = 475 In a particular section of Class IX, 40 students were asked about the months of their birth and the following graph was prepared for the data so obtained: ( ii ) Number of families having 1 girl = 814 Question 3: ( iii) Number of families having no girl = 211 Therefore, the sum of all these probabilities is 1. Page 3 Cbse-spot.blogspot.com 1 Class IX Chapter 15 – Probability Maths Exercise 15.1 Question 1: In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays. Find the probability that she did not hit a boundary. Answer: Number of times the batswoman hits a boundary = 6 Total number of balls played = 30 Number of times that the batswoman does not hit a boundary = 30 - 6 = 24 Question 2: 1500 families with 2 children were selected randomly, and the following data were recorded: Number of girls in a family 2 1 0 Number of families 475 814 211 Compute the probability of a family, chosen at random, having (i) 2 girls (ii) 1 girl (iii) No girl Also check whether the sum of these probabilities is 1. Cbse-spot.blogspot.com 2 Answer: Total number of families = 475 + 814 + 211 = 1500 (i) Number of families having 2 girls = 475 In a particular section of Class IX, 40 students were asked about the months of their birth and the following graph was prepared for the data so obtained: ( ii ) Number of families having 1 girl = 814 Question 3: ( iii) Number of families having no girl = 211 Therefore, the sum of all these probabilities is 1. Cbse-spot.blogspot.com 3 Find the probability that a student of the class was born in August. Answer: different outcomes: Outcome 3 heads 2 heads 1 head No head Frequency 23 72 77 28 If the three coins are simultaneously tossed again, compute the probability of 2 heads coming up. Answer: Number of times 2 heads come up = 72 Number of studen ts born in the month of August = 6 Three coins are tossed simultaneously 200 times with the following frequencies of Total number of students = 40 Question 4: Page 4 Cbse-spot.blogspot.com 1 Class IX Chapter 15 – Probability Maths Exercise 15.1 Question 1: In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays. Find the probability that she did not hit a boundary. Answer: Number of times the batswoman hits a boundary = 6 Total number of balls played = 30 Number of times that the batswoman does not hit a boundary = 30 - 6 = 24 Question 2: 1500 families with 2 children were selected randomly, and the following data were recorded: Number of girls in a family 2 1 0 Number of families 475 814 211 Compute the probability of a family, chosen at random, having (i) 2 girls (ii) 1 girl (iii) No girl Also check whether the sum of these probabilities is 1. Cbse-spot.blogspot.com 2 Answer: Total number of families = 475 + 814 + 211 = 1500 (i) Number of families having 2 girls = 475 In a particular section of Class IX, 40 students were asked about the months of their birth and the following graph was prepared for the data so obtained: ( ii ) Number of families having 1 girl = 814 Question 3: ( iii) Number of families having no girl = 211 Therefore, the sum of all these probabilities is 1. Cbse-spot.blogspot.com 3 Find the probability that a student of the class was born in August. Answer: different outcomes: Outcome 3 heads 2 heads 1 head No head Frequency 23 72 77 28 If the three coins are simultaneously tossed again, compute the probability of 2 heads coming up. Answer: Number of times 2 heads come up = 72 Number of studen ts born in the month of August = 6 Three coins are tossed simultaneously 200 times with the following frequencies of Total number of students = 40 Question 4: Cbse-spot.blogspot.com 4 Total number of times the coins were tossed = 200 Question 5: An organization selected 2400 families at random and surveyed them to determine a relationship between income level and the number of vehicles in a family. The information gathered is listed in the table below: Monthly income (in Rs) Vehicles per family 0 1 2 Above 2 Less than 7000 10 160 25 0 7000 - 10000 0 305 27 2 10000 - 13000 1 535 29 1 13000 - 16000 2 469 59 25 16000 or more 1 579 82 88 Suppose a family is chosen, find the probability that the family chosen is (i) earning Rs 10000 - 13000 per month and owning exactly 2 vehicles. (ii) earning Rs 16000 or more per month and owning exactly 1 vehicle. (iii) earning less than Rs 7000 per month and does not own any vehicle. (iv) earning Rs 13000 - 16000 per month and owning more than 2 vehicles. (v) owning not more than 1 vehicle. Answer: Page 5 Cbse-spot.blogspot.com 1 Class IX Chapter 15 – Probability Maths Exercise 15.1 Question 1: In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays. Find the probability that she did not hit a boundary. Answer: Number of times the batswoman hits a boundary = 6 Total number of balls played = 30 Number of times that the batswoman does not hit a boundary = 30 - 6 = 24 Question 2: 1500 families with 2 children were selected randomly, and the following data were recorded: Number of girls in a family 2 1 0 Number of families 475 814 211 Compute the probability of a family, chosen at random, having (i) 2 girls (ii) 1 girl (iii) No girl Also check whether the sum of these probabilities is 1. Cbse-spot.blogspot.com 2 Answer: Total number of families = 475 + 814 + 211 = 1500 (i) Number of families having 2 girls = 475 In a particular section of Class IX, 40 students were asked about the months of their birth and the following graph was prepared for the data so obtained: ( ii ) Number of families having 1 girl = 814 Question 3: ( iii) Number of families having no girl = 211 Therefore, the sum of all these probabilities is 1. Cbse-spot.blogspot.com 3 Find the probability that a student of the class was born in August. Answer: different outcomes: Outcome 3 heads 2 heads 1 head No head Frequency 23 72 77 28 If the three coins are simultaneously tossed again, compute the probability of 2 heads coming up. Answer: Number of times 2 heads come up = 72 Number of studen ts born in the month of August = 6 Three coins are tossed simultaneously 200 times with the following frequencies of Total number of students = 40 Question 4: Cbse-spot.blogspot.com 4 Total number of times the coins were tossed = 200 Question 5: An organization selected 2400 families at random and surveyed them to determine a relationship between income level and the number of vehicles in a family. The information gathered is listed in the table below: Monthly income (in Rs) Vehicles per family 0 1 2 Above 2 Less than 7000 10 160 25 0 7000 - 10000 0 305 27 2 10000 - 13000 1 535 29 1 13000 - 16000 2 469 59 25 16000 or more 1 579 82 88 Suppose a family is chosen, find the probability that the family chosen is (i) earning Rs 10000 - 13000 per month and owning exactly 2 vehicles. (ii) earning Rs 16000 or more per month and owning exactly 1 vehicle. (iii) earning less than Rs 7000 per month and does not own any vehicle. (iv) earning Rs 13000 - 16000 per month and owning more than 2 vehicles. (v) owning not more than 1 vehicle. Answer: Cbse-spot.blogspot.com 5 Number of total families surveyed = 10 + 160 + 25 + 0 + 0 + 305 + 27 + 2 + 1 + 535 + 29 + 1 + 2 + 469 + 59 + 25 + 1 + 579 + 82 + 88 = 2400 (i) Number of families earning Rs 10000 - 13000 per month and owning exactly 2 vehicles = 29 Hence, required probability, (ii) Number of families earning Rs 16000 or more per month and owning exactly 1 vehicle = 579 Hence, required probability, (iii) Number of families earning less than Rs 7000 per month and does not own any vehicle = 10 Hence, required probability, (iv) Number of families earning Rs 13000 - 16000 per month and owning more than 2 vehicles = 25 Hence, required probability, (v) Number of families owning not more than 1 vehicle = 10 + 160 + 0 + 305 + 1 + 535 + 2 + 469 + 1 + 579 = 2062 Hence, required probability, Question 6: A teacher wanted to analyse the performance of two sections of students in a mathematics test of 100 marks. Looking at their performances, she found that a few students got under 20 marks and a few got 70 marks or above. So she decided to group them into intervals of varying sizes as follows: 0 - 20, 20 - 30… 60 - 70, 70 - 100. Then she formed the following table:Read More

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