Question

Mr. Singh is paid as per the number of hours he puts in per month. The rate of pay was increased by 20% per hour, but the number of hours put in by him went down by 20%. What is the percentage increase / decrease in his income?

Answer 1

Let the amount paid be x and hours he put be y.
Then, his old income=xy
And now,
New amount paid=x+20x/100
=6x/5
And no. of hours he put now=y-y/5
=4y/5
So, his new income=24xy/25
Percentage change
=(24xy/25 - xy)/xy *100
=(-xy/25)/xy *100
=(-1/25) *100
=(-4%)

So, his income is decreased by 4%.