Tips and Tricks and Shortcuts for Number System

Type 1: Tips and Tricks for Number System & General questions

Question 1 Which one of the following is not a prime number?

Options

A. 51

B. 23

C. 17

D. 11

Solution:     51 is divisible by 17. So, it is not a prime number.

Correct option: A

Question 2. How many prime numbers are there from 1 to 50?

Options

A. 20

B. 15

C. 21

D. 25

Solution:    Prime numbers less than 50 are:

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47

Correct option: B

Question 3 1198 * 1198 = ?

Options

A. 1435204

B. 1432504

C. 1453204

D. 1435024

Solution:     (1198)²

(1200 – 2)²

We can use the identity: (a-b)²= a² + b² – 2ab

(1200)² + 2² – 2 * 1200 * 2

1440000 + 4 – 4800

1435204

Correct option: A

Question 4. The sum of first five prime numbers is:

Options

A. 20

B. 28

C. 30

D. 25

Solution:     Sum of first five prime numbers is = 2+3+5+7+11 = 28

Correct option: B

Question 5. If x and y are odd numbers, then which of the following is always an even numbers?

Options

A. x + y

B. xy

C. x/y

D. xy + 2

Solution:    The sum of two odd number is always even. So, x + y is even.

Correct option: A