Question

Determine the sum of all the prime numbers from 60 to 80

Answer 1

There are 21 numbers from 60 to 80 both terms inclusive.

We ignore all even numbers in this range as even numbers can not be prime.

The odd numbers are 61,63,65,67,69,71.73,75,77,79. The numbers in bold 63,65,69,75,77 are composite numbers as they have factors.

So remaining numbers are prime. They are 61,67,71,73,79.

So there are 5 prime numbers in this range.

Answer 2

Answer:

Determine the sum of all prime numbers from 60 to 80