Q1. What is the number of fives used in numbering a 260-page book? (2024)
(a) 55
(b) 56
(c) 57
(d) 60
Ans: (b)
From 1 to 100, 5 comes 20 times.
Similarly, from 101 to 200, 5 comes 20 times.
Similarly, from 201 to 300, 5 comes 20 times.
So, we just need to check the numbers after 260. Such numbers having 5 are 265, 275, 285, 295 i.e. 4 numbers.
So, the number of 5’s used from 1 to 260 = (20 + 20 + 20) - 4 = 56
Q2. Three numbers x, y, z are selected from the set of the first seven natural numbers such that x > 2y > 3z. How many such distinct triplets (x, y, z) are possible? (2024)
(a) One triplet
(b) Two triplets
(c) Three triplets
(d) Four triplets
Ans: (d)
4 triplets satisfying the given conditions are: (5,2,1), (6,2,1), (7,2,1) and (7,3,1)
Q3. Let x be a positive integer such that 7x + 96 is divisible by x. How many values of x are possible? (2023)
(a) 10
(b) 11
(c) 12
(d) Infinitely many
Ans: (c)
7x + 96 is divisible by x. It means that 96 is divisible by x, or x is a factor of 96.
96 = 25 × 3
So, x can be 1, 3, 2, 4, 8, 16, 32, 6, 12, 24, 48, and 96. So, a total of 12 possible values.
Hence, option (c) is correct.
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