Two pipes P and Q can fill a cistern in 4 min, and 6 min, respectively, If these pipes are opened on alternatively starting with P for one minute each, how long (in min.) will it take to fill the cistern?

A

$$4\frac{1}{3}$$

B

$$4\frac{2}{3}$$

C

$$5\frac{1}{4}$$

D

$$5\frac{1}{3}$$