SOLUTION: Jack usually mows his lawn in 3 hours. Jill can mow the same yard in 4 hours. How much time would it take for them to mow the yard together?

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Question 280398: Jack usually mows his lawn in 3 hours. Jill can mow the same yard in 4 hours. How much time would it take for them to mow the yard together?
Found 3 solutions by richwmiller, dabanfield, J.A.Romero:
Answer by richwmiller(17219)   (Show Source):
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Of course they must each have their own mower and not get in each other's way.
What size ranch are they mowing? Are they using scissors?
x/3+x/4=1
4x+3x=12
7x=12
x=12/7
x=1 5/7 hours about 1 hour 42 minutes 51 sec.
12/7/3+12/7/4=1
4/7+3/7=1
Jack does 4/7 and Jill does 3/7 of the job

Answer by dabanfield(803)   (Show Source):
You can put this solution on YOUR website!
Jack usually mows his lawn in 3 hours. Jill can mow the same yard in 4 hours. How much time would it take for them to mow the yard together?
The amount of lawn mowed is the product of the rate of mowing and the elapsed time (i.e. m = r*t).
Jack's rate of mowing is 1/3. Jill's ratre is 1/4. So their combines rate of mowing is 1/3 + 1/4. Let t be the ime needed. Then we have for mowing 1 lawn:
1 = (1/3 + 1/4)*t
1 = (4/12 + 3/12)*t
1 = (7/12)*t
t = 1/(7/12)
t = 1*(12/7)
t = 12/7 hours

Answer by J.A.Romero(2)   (Show Source):
You can put this solution on YOUR website!
x/3+x/4=1Job
LCD=3*4=12
4x+3x=12
7x=12
12/7=x