Question

Sum of the first three prime numbers which end at 3 is
A. \[20\]
B. \[16\]
C. \[39\]
D. \[40\]

Answer 1

Hint: In this question, we are asked to find out the sum of the first three prime numbers which end at \[3\].
First, we shall learn the concept of a prime number. A prime number is nothing but a number containing only two factors \[1\] and itself.
Firstly, we need to find out the first three prime numbers whose unit digit is \[3\] and we need to take out their sum.
We need to think about the two numbers whose product will be obtained as the new number which is ended by \[3\].

Complete step by step solution:
First, we will understand what exactly is meant by the prime number
So, a prime number is that number that has only two factors \[1\] and the number itself like $2$ , $3$ , $5$ , $7$ , $11$ , $13$ , $17$ , etc
Let the three prime numbers ending with \[3\] be $x$ , $y$ , $z$
We know that prime numbers ending with 3 are as follows
$3$, $13$, $23$ , $43$ etc
We need to find the sum of the first three prime numbers. So according to the list given above, we find that
\[
  x = 3 \\
  y = 13 \\
  z = 23 \\
 \]
So,
The Sum of the first three prime numbers ending with \[3\] \[ = x + y + z\]
\[ = 3 + 13 + 23\]
\[ = 39\]
Therefore, the correct option is (C)

Note: Students need to avoid calculation mistakes to find correct answers. Calculation mistakes always lead them to incorrect answers.
Option A,B,D are the incorrect answers as during solving the sum we have not to find them. They can directly eliminate other options while solving the sum.
Students must not be confused between prime and composite numbers. The number with only two factors is a prime number and the number with more than two factors is composite and \[1\] is neither a prime nor a composite number.