- A15
- B20
- C18
- D25
Step-by-Step Solution
18 = and , so it is a multiple of both 2 and 3 and is struck once in each round. 15 is a multiple of 3 only, 20 of 2 only, and 25 survives both rounds — it leaves later, with the multiples of 5.
Answer: C) 18
Rehan sieves the numbers 1 to 30. He crosses off every multiple of 2 except 2 itself, then every multiple of 3 except 3 itself. Which number gets crossed off TWICE?
Class 6Playing with NumbersPlaying with Numbers
Key idea: Multiples are unlimited
The multiples of 7 are 7, 14, 21, 28, 35, … — you get them by multiplying 7 by 1, 2, 3, 4, 5, …. Multiples never run out. Every number is a multiple of itself (and of 1). 0 is a multiple of every number, but we usually exclude it when listing multiples for practical work.
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