Page 47 - Math Skill - 5

Factors and Multiples 45

Exercise 4.1

1. Can 12 and 35 be called co-prime numbers? Why?
2. Which of the following numbers are divisible by 2?
(a) 12 (b) 15 (c) 45376 (d) 325984

3. Test the divisibility of these numbers by 3 without performing actual division.
(a) 126 (b) 732 (c) 2318 (d) 59403

4. Which of the following numbers are divisible by 4?
(a) 114 (b) 7718 (c) 440880 (d) 83257943

5. Test the divisibility of the following numbers by 5.
(a) 1650 (b) 3785 (c) 7778 (d) 38125
(e) 70050 (f) 35551 (g) 202020 (h) 3535350

6. Test whether the following numbers are divisible by 6.
(a) 7050 (b) 32832 (c) 46012 (d) 42756

7. Test whether the following numbers are divisible by any one or two or all of 7, 8 and 9.
(a) 14456 (b) 854 (c) 5679 (d) 2618859

Prime Factorisation

When a given number is expressed as the product of prime numbers, then the method is called
prime factorisation. We can find the prime factors by:

(a) Factor tree method
(b) Division method

Factor Tree Method

Let us consider a number 315 and find out its prime factors using the tree method.

Or
315 315

5 × 63 3 × 105

7 × 9 3 × 35

3 × 3 5 × 7

315 = 5 × 7 × 3 × 3

Numbers in circles show the prime factors of 315. They are same in both the figures. Only the
arrangement or order is different.