Page 86 - ICSE Math 4

2. Circle the odd mul ples and underline the even mul ples of the given coloured
numbers.
(a) 3 21 27 30 39 42 45

(b) 4 24 28 32 36 40 44
(c) 5 25 30 35 40 45 50

(d) 6 24 30 36 42 48 54

3. Write all the prime numbers less than 50.

4. Write all the composite numbers between 30 and 70.

5. Find whether the given numbers are prime or composite.

(a) 67 (b) 113 (c) 137

(d) 123 (e) 71 (f) 125

6. Find the prime factors of the following numbers by factor tree method.

(a) 24 (b) 52 (c) 16

(d) 12 (e) 45 (f) 36

7. Find the prime factors of the following numbers by prime factoriza on method.
(a) 63 (b) 108 (c) 314

(d) 96 (e) 280 (f) 121

8. Complete the sequences given below.
(a) 1, 3, 5, 7, ___ , ___ , ___ , ___ , ___ (Hint: Odd numbers)

(b) 2, 4, 6, 8, ___ , ___ , ___ , ___ , ___ (Hint: Even numbers)

(c) 2, 3, 5, 7, ___ , ___ , ___ , ___ , ___ (Hint: Prime numbers)

(d) 4, 6, 8, 9, ___ , ___ , ___ , ___ , ___ (Hint: Composite numbers)

Tests of Divisibility of Numbers

Divisibility test is a test or a rule which helps us to know whether one number is divisible
by another number or not.

For example, 14 is divisible by 2 because 14  2 = 7 remainder 0. 13 is not divisible by 2
since 13  2 = 6 with remainder 1.
Top Tip
This test helps us to fi nd the factors of large numbers.
Let’s see and use some divisibility rules to fi nd if a number Every number is
divisible by 1.
is divisible by 2, 3, 4, 5, 9 and 10, without doing much
calcula ons.

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