Question 1114844
One pipe can fill a pool in 10 hours.
 Another pipe can fill the pool in 30 hours.
 How long would it take them to fill the pool if they were working together?
:
Let t = time required with both pipes work together
let the completed job = 1 (a full pool)
:
Each will do a fraction of the job, the two fractions add up to 1
:
{{{t/10}}} +| {{{t/30}}} = 1
multiply equation by 30, get rid of the denominators
30*{{{t/10}}} +  30*{{{t/30}}} = 30(1)
cancel
3t + t = 30
4t = 30
t = {{{30/4}}}
t = 7.5 hrs working together