SOLUTION :
Let the number be 100.
∵ Increase in number = 25% of 100 =25 /100 x 100 = 25
∴ Increased number = 100 + 25 = 125
When increased no. = 125, the original no. = 100
When increased no. = 1, the original no. = 100 / 125
When increased no. = 150,
The original no. = 100 / 125 × 150 = 120 ;Ans