how do solve percentage question

Percentage Change = (Final Value – Initial Value)/Initial Value * 100

For two successive changes of of x% and y%, the total % change is (x + y + xy/100)%

If A is x% more than B then B is x%/(1+x%) less than A.

For e.g.
If A is 20% more than B then B is 20%/120% = 16.66% less than A.

The sum of the number of boys and girls in a school is 150. If the number of boys is x, then the number of girls becomes x% of the total number of students. The number of boys is:

If girls are x% of the total number of students, boys will be 1-x% of the students. Hence, x/150 = 1-x%. Hence, x = 150 - 150x/100. Hence, 2.5x =150. Hence, x=60.

Thus, there are 60 boys.

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