<PRE><B>Question 619272</B>
A roofer requires 15 hours to shingle a roof. And apprentics roofer can do tthe job in 21 hours. How long would it take to shingle the roof if they work together?
------
roofer rate: 1/15 job/hr
apprentice rate: 1/21 job/hr
---
Together rate: 1/x job/hr
------
Equation:
rate + rate = together rate
1/15 + 1/21 = 1/x
----
21x + 15x = 15*21
---
36x = 15*21
x = (5/12)21
x = (5/4)7
x = 35/4 = 8 3/4 hrs (time to do the job together)
=====================
Cheers,
Stan H.
========================
</PRE>