Every Saturday, Mary mows her lawn. It takes he 4 hours to finish mowing if she works alone. This Saturday, however, Mary's friend Dominic said that he would help her. If together they are able to finish the lawn in 2 hours and 24 minutes, how long would it take Dominc to mow the lawn by himself?
2007-03-22 02:21:34 · 4 answers · asked by babigurl34 2 in Science & Mathematics ➔ Mathematics
mary mows at a rate of 1/4 lawns per hour
together they mow at rate of 1/2.4 lawns per hour
so dominic mows at rate of 1/2.4 - 1/4 = 5/12-1.4=1/6 lawn per hour
so dominic would take 6 hours on his own
2007-03-22 02:26:23 · answer #1 · answered by hustolemyname 6 · 0⤊ 0⤋
These questions are annoying.
You make the assumption that both of these guys work at the same rate, whether they work by themselves or together. So start by finding the ratio of time it takes between working together and alone.
2 hours 24 minutes = 144 minutes
4 hours = 240 minutes
144/240 = 3/5
So Mary did 3/5 of the lawn in 3/5 the amount of time...makes sense. That means that Dominic takes is able to do 2/5 of the lawn in 144 minutes.
(2/5)x = 144
x = 360 minutes
It takes him 360 minutes, or 6 hours, to do the lawn by himself
2007-03-22 09:28:30 · answer #2 · answered by Bhajun Singh 4 · 0⤊ 0⤋
If we let the amount of area of the lawn be a, then Mary can mow a/4 in an hour.
However, she only mows for 2hrs 24min (2.4hrs). Her friend Dominic also mows for 2.4hrs (as in the question) Together, their combined mowed area add up to a (the original area of the lawn)
If we let the time it takes Dominic to mow the lawn be 't'
2.4 (a/4) + 2.4 (a/t) = a
0.6a + 2.4a/t =a
2.4a/t = a - 0.6a
2.4a/t = a (1 - 0.6)
2.4a/t = 0.4a
t = 2.4a/0.4a
t = 6
Therefore, it would take Dominic 6hrs to mow the lawn by himself. Hope you get that
2007-03-22 09:41:09 · answer #3 · answered by JJ 2 · 1⤊ 0⤋
both the guys have answered it - correctly too. Don't think my input is needed.
2007-03-22 09:34:10 · answer #4 · answered by sanjay 4 · 0⤊ 0⤋