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After two successive increments, Gopal's salary became 187.5%187.5 \% of his initial salary. If the percentage of salary increase in the second increment was twice of that in the first increment, then the percentage of salary increase in the first increment was

Solution

✅ Correct Option: 2

Let the first increment =x%=x\%

Then the second increment =2x%=2x\%

The key insight here is that Gopal's salary became 187.5%187.5\% of his initial salary.

If his original salary was 100%100\%, then his salary increased by 87.5%87.5\% in total.


When we have successive percentage increases, we cannot simply add them together.

If your salary increases by 10%10\% first, then by 10%10\% next, the second increase is calculated on the already increased salary, not the original one. Hence, there is a compounding effect, and the total increase would be more than 20%20\%.


For two successive percentage changes a%a\% and b%b\%, the net percentage change is:

Net %\% change =a+b+a×b100= a + b + \tfrac{a \times b}{100}

The third term a×b100\tfrac{a \times b}{100} accounts for the compound effect.


We substitute our values:

a=xa = x

b=2xb = 2x

Net change =87.5%= 87.5\%

87.5=x+2x+x×2x10087.5 = x + 2x + \tfrac{x \times 2x}{100}

87.5=3x+x×2x10087.5 = 3x + \tfrac{x \times 2x}{100}

87.5=3x+x×x10087.5 = 3x + \tfrac{x \times x}{100}

If we expand the equation, we will have to solve for the root. We can see there is 3x3x and can reasonably use x=25x = 25 to test.

75+25×2550=75+12.5=87.575 + \tfrac{25 \times 25}{50} = 75 + 12.5 = 87.5


Therefore, the percentage of salary increase in the first increment was 25%.

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