SOLUTION: Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 5 hours. How much time would it take for them to mow the lawn together?

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Question 315536: Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 5 hours. How much time would it take for them to mow the lawn together?

Found 2 solutions by stanbon, CharlesG2:
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 5 hours. How much time would it take for them to mow the lawn together?
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Jack DATA:
time = 3 hrs/job ; rate = 1/3 job/hr
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Marilyn DATA:
time = 5 hrs/job ; rate = 1/5 job/hr
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Together DATA:
time = x hrs/job ; rate = 1/x job/hr
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Equation:
rate + rate = together rate
1/3 + 1/5 = 1/x
---
5x + 3x = 15
8x = 15
x = 15/8 = 1.875 hrs (time to do the job together)
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Cheers,
Stan H.

Answer by CharlesG2(834) (Show Source):
You can put this solution on YOUR website!
Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 5 hours. How much time would it take for them to mow the lawn together?
this is a rate of work problem
let x = Jack's 3 hours
let y = Marilyn's 5 hours
time together for 2 people = 1/(1/x + 1/y)
time together for 2 people = 1/(1/3 + 1/5)
time together for 2 people = 1/(5/15 + 3/15) (equivalent fractions)
time together for 2 people = 1/(8/15)
time together for 2 people = 15/8 hours = 1.9 hours rounded to nearest tenth
9/10 of an hour is approximately 54 minutes