If each side of a square is increased by 20%, find the percentage increase in its area.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 44%
The area of a square is side × side, so a 20% rise in the side multiplies the area by \(1.2\times1.2\), not by 1.2.
Assuming the side to be 10:
Old area \(=10\times10=100\)
New side \(=12\), new area \(=12\times12=144\)
Increase \(=144-100=44\) on 100, that is, 44%
Tip: Two successive changes of \(a\%\) and \(b\%\) give a total change of \(\displaystyle a+b+\frac{ab}{100}\) per cent; here \(\displaystyle 20+20+\frac{400}{100}=44\%\).