In tow-digit number, the digit in the unit’s place is four times the digit in ten»s place and sum of the digits is equal to 10. What is the number?

A. 14
B. 18
C. 20
D. 28
Ans: D

Explanation:

Let the ten’s digits be x. Then, unit’s digit = 4x.
x + 4x = 10
5x = 10
x = 2.
So, ten’s digit = 2, unit’s digit = 8.
Hence, the required number is 28.