Description for Correct answer:
Part filled by both in 2 min = \( \Large 2x \left(\frac{1}{15}+\frac{1}{20}\right)=2x \left(\frac{4+3}{60}\right) \)

=\( \Large 2 \times \frac{7}{60}= \frac{7}{3} \)

Part unfilled = \( \Large 1 - \frac{7}{30}=\frac{30-7}{30}=\frac{23}{30} \)

Now, B fills \( \Large \frac{1}{20} \) part in 1 min.

Therefore, \( \Large \frac{23}{30} \) part will be filled by B In

= \( \Large \left(20 \times \frac{23}{30}\right)min\ or\ i\ \frac{46}{3}min \)

Therefore, Required time taken to fill the tank

=\( \Large \left(2+\frac{46}{3}\right)=\frac{52}{3}min. \)