need help with word problems

Question

It takes one crew 4 hours to clean an auditorium after an event. If a second crew helps, it only takes 2.5 hours. How long would it take the second crew, working alone, to clean the auditorium?

Answer 1

The trick t these things is setting up the problem in equation form and correctly assigning units to the variables.

Team A does 0.25 per hour  A = 0.25* aud / hr

Team A + B does 0.40/hr     A + B = 0.4 aud / hr

Subtract the first equation from the second equation

 

A = B = 0.4

A =        0.25

B = 0.4 - 0.25 = 0.15 aud/hr

 

Now chamge aud/hr to  hr/aud  aud/hr = 1/0.15 = 6.666...