Question

3. Jim can fill a pool carrying buckets of water in 30 minutes. Sue can do the same job in 45 minutes. Tony can do the same job in 1 ½ hours. How quickly can all three fill the pool together?

A. 12 minutes
B. 15 minutes
C. 21 minutes
D. 23 minutes
E. 28 minutes

Answer 1

These can be tricky. (To me at least!) I find that I can tackle these by summarizing each rate. Jim's rate is 1/30 (one thirtieth of a pool per minute). Sue's rate is 1/45 (one forty-fifth of a pool per minute). And Tony's rate is 1/90 (one ninetieth of a pool per minute). So if they worked together, their combined rate is: 1/30 + 1/45 + 1/90.
So the equation to solve is: time X rate = distance
Let's let T represent the amount of time it takes them to fill the pool working together.
And let's let "distance" stand for filling one full pool
T X (1/30 + 1/45 + 1/90) = 1
Then solve for T, which should be one of the choices offered.

Answer 2

looks right but explain hwo you got 1/90

Answer 3

Ah, sorry. The problem says Tony can do the job in 1-1/2 hours. The other folks' rates are in minutes, so I had to convert that to minutes. Doing the job in 1-1/2 hours is the same as saying Tony's rate is doing the job in 90 minutes. That means his rate is 1 pool filled in 90 minutes, or 1/90th of a pool per one minute. Make sense?

Answer 4

okey