SOLUTION: Frank can cut his lawn in 4 1/2 hours, his wife can cut the same lawn in 4 hours, while their son tom can cut the lawn in 3 1/2 hours. how long would it tak to cut the lawn if all

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Question 305049: Frank can cut his lawn in 4 1/2 hours, his wife can cut the same lawn in 4 hours, while their son tom can cut the lawn in 3 1/2 hours. how long would it tak to cut the lawn if all three worked together?
Sat prep. Question.
Ans. 252/191 hours
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Frank can cut his lawn in 4 1/2 hours, his wife can cut the same lawn in 4 hours, while their son tom can cut the lawn in 3 1/2 hours. how long would it take to cut the lawn if all three worked together?
:
Let t = time required when all three work together (with 3 lawn mowers)
:
let the completed job = 1; (a mown lawn)
:
t%2F4.5 + t%2F4 + t%2F3.5 = 1
:
Multiply equation by 252, results
56t + 63t + 72t = 252
191t = 252
t = 252%2F191, just like you had
t = 1.32 hrs working together