If a% of a is 81, then a is equal to:

The correct answer is Option (3) → 90

Per cent means hundredths, so \(a\%\) of \(a\) is \(\frac{a}{100}\times a=\frac{a^{2}}{100}\).

• This is given as 81: \(\displaystyle\frac{a^{2}}{100}=81\)

• \(a^{2}=8100\)

• \(a=90\), since \(90\times90=8100\)