Question

Find two pairs of prime numbers less than 20 that differ by 4

Answer 1

3 and 7,

7 and 11,

13 and 17

Explanation:

Prime numbers have exactly two factors, the number itself and 1. This just means that nothing "goes into" these numbers. Example: 7. 7 is a prime number; the only number that goes into 7 is 7 (and 1)

First, find all the prime numbers that are less than 20:

2, 3, 5, 7, 11, 13, 17, 19

Next find the pairs that are 4 units apart. 3 and 7 works.

7 - 3 is 4

Also, 13 and 17 works, and 7 and 11.