Directions (Set of 5 questions): What approximate value should come in place of the question marks(?) in the following questions? (Note : you are not expected to calculate the exact value.)
$\left( {{36.08}^{2}}-~{{17.81}^{2}} \right)\div 53.89\times \sqrt{?}=122.21~$
Solution
$\left( {{36.08}^{2}}-~{{17.81}^{2}} \right)\div 53.89\times \sqrt{?}=122.21~$
$\sqrt{?}~\approx \frac{54\times 122}{(36 + 18) (36 - 18)}$
$\sqrt{?}~\approx \frac{6588}{972}$ $\approx$ 6.77
$\sqrt{?}~\approx 7~$
$?=~{{7}^{2}}=49$