One tap fill a tank in 20 minute and another tap fill it in 12 minute . the tank being empty and if both tap are opened together in how many minutes the tank will be full?

15/2 or 7.5 minutes

Step-by-step explanation:

Tap 1 fill a part of tank in 1 minute = 1/20

Tap 2 fill a part of tank in 1 minute = 1/12

2 tap of tank fill in 1 minute = 1/12 + 1/20

= 2/ 15

So if both tap open, the tank will be filled in 1/(2/15) = 15/2 or 7.5 mins

Hope this help :3