Question

Instead of increasing a number by 25%, a student decreased that number by 25%, and then obtained number is increased by 25%. By what percent is his answer less than the original (correct) answer?
1. 25
2. 20
3. 12.5
4. 50

Answer 1

Correct Answer - Option 1 : 25

Calculation:

Let the number be 100

According to the question,

then correct Increased number = 100 x (100 + 25%)/100

⇒ 125

But by mistake he first decreased the number by 25%

⇒ 100 × (100 - 25%)/100 = 75

Then he Increased the result by 25%

⇒ 75 × (100 + 25)/100 = 375/4 = 93.75

Difference between original and new number = 125 - 93.75

⇒ 31.25

Required change % = (31.25/125) × 100 = 25%

∴ Required change % is 25%.