Q11 of 55 Page 53

Write five pairs of prime numbers below 20 whose sum is divisible by 5.

These are the pairs of prime numbers below 20 whose sum is divisible by 5;

2+3 = 5

3+7 = 10

7+13 = 20

17+3 = 20

19+11 = 30

Write seven consecutive composite numbers less than 100 so that there is no prime number between them.

Express each of the following numbers as the sum of three odd primes:

(a) 21 (b) 31

Fill in the blanks.

(a) A number which has only two factors is called a …………...

(b) A number which has more than two factors is called a ………………..

(d) The smallest prime number is …………...

(e) The smallest composite number is ………....

(f) The smallest even number is ……………....

Using divisibility tests, determine which of the following numbers are divisible by 2; by 3; by 5; by 6; by 8; by 9; by 10; by 11 (say, yes or no):

Questions · 55

3. Playing with Numbers

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