SOLUTION: A large and a small heating unit are being used to heat the water of a pool. The larger unit, working alone, requires 7 h to heat the pool. After both units have been operating for
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Question 976135: A large and a small heating unit are being used to heat the water of a pool. The larger unit, working alone, requires 7 h to heat the pool. After both units have been operating for 3 h, the larger unit is turned off. The small unit requires 11 h more to heat the pool. How long would it take the small unit, working alone, to heat the pool?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A large and a small heating unit are being used to heat the water of a pool.
The larger unit, working alone, requires 7 h to heat the pool.
After both units have been operating for 3 h, the larger unit is turned off.
The small unit requires 11 h more to heat the pool.
How long would it take the small unit, working alone, to heat the pool?
:
let s = time required by the small unit to heat the pool
let a completely heated pool = 1
:
Each unit will do a fraction of the work, the two fractions add up to 1
:
The small unit is on for a total of 14 hrs
+ = 1
multiply by 7s, cancel the denominators and you have
7(14) + 3s = 7s
98 = 7s - 3s
90 = 4s
s = 98/4
s = 24.5 hrs for the small unit alone
:
:
Check this
+ =
.57 + .43 = 1
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