Question

When we add fourth and fifth triangular number we get ______

(a) 5^2

(b) 6^2

(c) 25^2

(d) 25^3

I got this question by my school principal while I was bunking the class.

This intriguing question originated from Patterns in Squares of Numbers topic in portion Squares and Square Roots of Mathematics – Class 8

Answer 1

Right answer is (a) 5^2

Easiest explanation: The fourth and fifth triangular numbers are 10 & 15.

10 + 15 = 25 = 5^2. Therefore 5^2 is the correct answer and the other options are incorrect. The options should be read carefully as the options are very close.