A number leaves no remainder when it is divided by 10. Which pair of numbers must ALSO divide it exactly?

Class 6Playing with NumbersPlaying with Numbers

A2 and 5
B3 and 4
C4 and 6
D5 and 9

Step-by-Step Solution

10 =

2 \times 5

, so whatever 10 divides is divisible by 2 and by 5 as well — for instance 70 ÷ 2 = 35 and 70 ÷ 5 = 14. The trap is assuming a multiple of 10 must also be a multiple of 3, 4, 6 or 9: 70 fails all four of those.

Answer: A) 2 and 5

Key idea: HCF and LCM — the two ends of common ground

**HCF** (Highest Common Factor) is the biggest number that divides both numbers — it sits at the *small* end of common factors. **LCM** (Least Common Multiple) is the smallest number both numbers divide — it sits at the *small* end of common multiples (which is the *big* side of factors). For Class 6, the simplest method is listing: write all the factors (or first several multiples) of each number and pick the right one. Faster methods come in Class 7.

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