Easy
Three of the following four numbers are alike in a certain way and one is different. Find the different one: 81, 100, 125, 144
Explanation
Explanation
81 (9 squared), 100 (10 squared) and 144 (12 squared) are all perfect squares. 125 is not a perfect square (it is a perfect cube, 5 cubed), so 125 is the odd one out.
PRO TIP
Re-check your working by substituting the answer back into the original question.