Expert: Scott A Wilson - 7/17/2010

Question
It takes a worker 3 hours to do a job. With a partner it takes 1 and a half hours. How long for the partner to do it alone. The answer is 3 I just having trouble writing it on paper... Another one is it takes 2 pumps to fill a tank 21 min. One pumps 3 times faster. In my head I see the numbers 3 and 1 which also equal 4. 21 x 3 is the faster one. 21 x 4 the other. I'm hauing problems writing this too? Could help me with writing them both? Thanks.

Answer
With two of them, the time is cut in half, so the other must work at the same rate,
so yes, the answer is known.

The first worker, A, would do 2 jobs in 6 hours.
Together that would do 4 jobs in 6 hours.
Then take 4 - 2 = 2, and this is the amount of jobs the other could do in 6 hours.

On the tanks, it takes the first pump 21 minutes to fill a tank and the other is 3 times faster.
This means the other can do it in 7 minutes, so the other can fil 3 tanks in 21 minutes.
This means that both of them can fill 4 tanks in 21 minutes.
From this, it can be seen that working together takes 21/4 minutes,

and that should come out to 5.25.