Question 166862
Let's deal in minutes

Let x=amount of time it takes all three working together to fill the pool
Jim fills at the rate of 1/30 pool per min
Sue fills at the rate of 1/45 pool per min
Tony fills at the rate of 1/90 pool per min

Together they fill at the rate of 1/30 + 1/45 + 1/90=
3/90 + 2/90 + 1/90=6/90 =1/15 pool per min, so our equation to solve is:
(1/15)x=1 (1 pool that is)  multiply each term by 15
x=15 min-------------------- time it takes all three working together 

CK
Jim:  (1/30)*15=1/2
Sue:  (1/45)*15=1/3
Tony  (1/90)*15=1/6
1/2 +1/3 +1/6 =3/6 + 2/6 + 1/6=6/6
1=1


Hope this helps---ptaylor