SOLUTION: One lawn care woker can mow 3 lawns in 60 min. and another can mow 5 lawns in 75 min. How long will it take them to mow 7 lawns together?

Question 219900: One lawn care woker can mow 3 lawns in 60 min. and another can mow 5 lawns in 75 min. How long will it take them to mow 7 lawns together?
Found 2 solutions by stanbon, josmiceli:
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
One lawn care woker can mow 3 lawns in 60 min. and another can mow 5 lawns in 75 min. How long will it take them to mow 7 lawns together?
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Let "the job" be 1 lawn mowed
Our Man DATA:
time = 20 min/job ; rate = 1/20 job/min
-------------------------------------------
Other Man DATA:
time = 15 min/job ; rate = 1/15 job/min
--------------------------------------------
Together DATA:
time = x min/job ; rate = 1/x job/min
---------------------------------------
Equation:
rate + rate = together rate
1/20 + 1/15 = 1/x
Multiply thru by 60x to get:
3x + 4x = 60
7x = 60
x = 60/7 minutes (time for both working together to mow one lawn)
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Time to mow 7 lawns = 7(60/7) = 60 minutes or one hour
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Cheers,
Stan H.

Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
This is a rate problem
In general:
(1st worker's rate) + (2nd worker's rate) = (rate working together)
given:
1st worker's rate = lawns/min
2nd worker's rate = lawns/min

Multiply both sides by

min
It takes them 1 hr to mow 7 lawns working together

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