According to the formula, if pipe A can comletely fill a tank in x hours and pipe B can comletely fill a tank in y hours, then the time taken by both pipes together to fill the tank is $\frac{\mathrm{xy}}{\mathrm{x}+\mathrm{y}}$ hours.

So, $\frac{2\times 3}{2+3}=\frac{6}{5}=1.2 \mathrm{hours}$

The tank will be filled by both the pipe when opened simultaneously in 1.2 hours

Hence option B is correct.