Q10 of 55 Page 53

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

(a) 21 (b) 31


(c) 53 (d) 61

(a) 21 = 5 + 5 + 11


Clearly, 5 and 11 are prime numbers.


(b) 31 = 5 + 7 + 19


Clearly, 3, 7 and 19 are prime numbers.


(c) 53 = 5 + 17 + 31


Clearly, 5, 17 and 31 are prime numbers.


(d) 61 = 13 + 17 + 31


Clearly, 13, 17 and 31 are prime numbers.


More from this chapter

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8

Which of the following numbers are prime?

(a) 23 (b) 51


(c) 37 (d) 26

 9

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

 11

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

 12

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 ………………..


(c) 1 is neither …………….. nor …………….


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


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


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