Question

A positive integer is subtracted from its square. The units digit of the result could be which of the following?

a. 3
b. 4
c. 5
d. 6
e. 7

Answer 1

Correct answer is D.

Look at the unit digit of a number, and ignore the other digits. We will denote other digits with dots (......). Let's say we have a number .....3.

......3^2 - 3 = ......9 - 3 = ........6

Check for numbers which unit digit is 1,2,4,5,6,7,8,or 9. They don't satisfy any of the answer options.