Write out the common factors of 28 and 42. How many common factors do the two numbers have?

Class 6Playing with NumbersPlaying with Numbers

Step-by-Step Solution

Factors of 28: 1, 2, 4, 7, 14, 28. Factors of 42: 1, 2, 3, 6, 7, 14, 21, 42. The ones in both lists are 1, 2, 7 and 14 — four of them, the biggest being the HCF, 14. The trap is dropping 1, which is a common factor of every pair of numbers.

Answer: B) 4

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.

Master this chapter in 30 minutes a day.

Don't just memorise the answer — build a daily practice habit.

Practice 5 Similar Questions Free →

All Playing with Numbers practice questions

More Class 6 Playing with Numbers practice

Which number below is a common multiple of 6 and 8 but is NOT the LCM of 6 and 8?Find the HCF of 72 and 108 by prime factorisation.Find the LCM of 24 and 90 using prime factorisation.Use the division method on 132 and 220 — divide the larger by the smaller, then keep…The HCF of 18 and 24 is 6. Use the rule HCF × LCM = product of the two numbers to work…