Posted by shirley on .
if a person can fill a tank in 12 min. and another person can fill a tank in 20 min. How long will it take both of them to fill 1 tank together?

math 
JJ,
12/60 = 1/5 of an hour
1 tank can be filled in 1/5 of an hour
your rate is 5 tanks per hour
20/60 = 1/3 of an hour
The tank can be filled in 1/3 of an hour. your rate is 3 tanks per hour
(5 tanks per hour)time + (3 tanks per hour)time = 1 tank filled
5t + 3t = 1
t =1/8 of an hour.
This makes sense because it should take less time to fill the tank if both are working together.