The sum of four consecutive two-digit odd numbers, when divided by 10, becomes a perfect square. Which of the following can possibly be one of these four numbers?

1) 21

2) 25

3) 41

4) 67

5) 73

Answer is A

As 21+22+23+24=90.

90/10=9 Which is a perfect square.

This problem can be easily done by Trial and error method.

First Estimate the sum of any 4 numbers around the given number.

Then Divide the sum by 10

Find if it is near a perfect square

Now Use Trial and error method to find the number isf neccessary