Numbers-18 (CAT-2003ii)

If a,a+2,a+4 are prime numbers, then the number of possible solutions for a is:

(1)   one                  (2) two            (3) three         (4) more than three

Solution follows here:

Solution:

Prime numbers start from 2. Except 2, no other prime number is even. So we need to consider three consecutive odd numbers here.

The only possible triad is 3,5,7. Excepting this case, one number out of any three consecutive odd numbers is a multiple of three and hence won’t be a prime.

Answer (1)