Question

The sum of the first five prime numbers is:
(a).11
(b).18
(c).26
(d).28

Answer 1

Hint: First of all we need to know which are the prime numbers . Then we need to find the first five prime numbers and then calculate the sum of these numbers.

Complete step-by-step answer:
The definition of prime numbers says that any number which has only two factors i.e. 1 and the number themselves. And there is no absolute method to check if a number is prime or not. We ourselves have to think about the factors that a given number could have.

Let us start from 1. 1 has only 1 factor i.e. 1 itself. Therefore, it is not prime.

Next we have 2, 2=2x1 has two factors 1 and 2 itself. Therefore, it is prime.
3, 3=3x1 has only two factors 3 and 1 therefore it is also prime.
4, 4=2x2=4x1 has 3 factors 1,2 and 4 therefore it is not prime.
5, 5=5x1 has only two factors 5 and 1 therefore it is prime.
6, 6=3x2=6x1 has 4 factors 1,2,3 and 6 itself therefore it is not prime.
7, 7=7x1 has only two factors 7 and 1 therefore it is prime.
8, 8=2x4=1x8 has 4 factors 1,2,4 and 8 therefore it is not prime.
For 9 we have,9=3x3=1x9 has 3 factors 1,3 and 9 therefore it is not prime.
10=2x5=1x10, has factors 1,2,5 and 10 hence, is also not prime.
11=1x11, has only two factors therefore it is prime.

So our first 5 prime numbers are 2,3,5,7,11.

Sum of all these are $2+3+5+7+11=28$

Hence, the answer is 28.

Note: Every even number is a composite number except 2 because every even number has minimum three factors 1,2 and the number themselves but 2 has only two factors 1 and 2.