When water is changed into ice, its volume increases by 9%. If ice change into water, the percentage decrease in volume is :

Answer: Option A

Let V denote the volume of 1 c.c. of water
Then, volume of ice formed from it :
= 109% of V = $$\frac{109}{100}$$V
When this ice change into water, decrease in volume :
= $$\frac{109}{100}$$V - V = $$\frac{9}{100}$$V
∴ Decrease % :
$$\begin{array}{rl}& =\left(\frac{9V}{100}\times \frac{100}{109V}\times 100\right)\%\\ & =\frac{900}{109}\%\\ & =8\frac{28}{109}\%\end{array}$$