Question

Question 10 (a)

Express the given number as the sum of three odd primes:
21

Answer 1

To obtain an odd number like 21, the possible combinations are : odd + odd + odd = odd
even + even + odd = odd

Our second case fails because we only have 2 as an even prime number.

So, the only case is : odd + odd + odd = odd.

Clearly, 3 + 7 + 11 = 21
Here 3, 7, and 11 are odd prime numbers.