$$\sqrt {\frac{{0.081 \times 0.484}}{{0.0064 \times 6.25}}} {\text{ }}$$   is equal to ?

Sum of decimal places in the numerator and denominator under the radical sign being the same, we remove the decimal.
∴ Given expression,
$$\eqalign{ & = \sqrt {\frac{{0.081 \times 0.484}}{{0.0064 \times 6.25}}} \cr & = \sqrt {\frac{{81 \times 484}}{{64 \times 625}}} \cr & = \frac{{9 \times 22}}{{8 \times 25}} \cr & = 0.99 \cr} $$