SOLUTION: my question is a word problem that I can't solve which is this: Jack usually mows his lawn in 7 hours.Marilyn can mow the same yard in 5 hours. How much time would it take for the

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Question 850604: my question is a word problem that I can't solve which is this:
Jack usually mows his lawn in 7 hours.Marilyn can mow the same yard in 5 hours. How much time would it take for them to mow the lawn together?
Found 3 solutions by unlockmath, josmiceli, richwmiller:
Answer by unlockmath(1688) About Me  (Show Source):
You can put this solution on YOUR website!
Hello,
There's a couple ways to set up this, here's one way:
t/7 +t/5 = 1
Multiply by 35 to get:
5t + 7t = 35
12t = 35
t= 35/12 or 2.9 hours
Make sense?
RJ
www.math-unlock.com

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of mowing to get
their rate mowing together
Jack's rate:
( 1 lawn mowed ) / ( 7 hrs )
Marilyn's rate:
( 1 lawn mowed ) / ( 5 hrs )
------------------------
Let +t+ = time in hours for them
to mow the lawn working together
+1%2F7+%2B+1%2F5++=+1%2Ft+
Multiply both sides by +35t+
+5t+%2B+7t+=+35+
+12t+=+35+
+t+=+2.+9167+
+.9167%2A60+=+55+
It will take them 2 hrs and 55 min mowing together
check:
+1%2F7+%2B+1%2F5++=+1%2Ft+
+1%2F7+%2B+1%2F5++=+1%2F2.9167+
+.14286+%2B+.2+=+.34285+
+.34286+=+.34285+
close enough

Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
1/7*60+1/5*60=1/t
t = 175 minutes
180 minutes is three hours
t=2 hours 55 minutes