Carcass wrote:
Renee can mow a lawn in 2 hours, and Jeremy can mow the same lawn in 1 hour and 15 minutes. If Renee starts mowing the lawn at 2:00 P.M., and Jeremy starts helping her at 2:30 P.M., at what time will they finish mowing the lawn, rounded to the nearest minute?
A. 2:35 P.M.
B. 2:50 P.M.
C. 3:05 P.M.
D. 3:25 P.M.
E. 3:55 P.M.
Kudos for the right answer and explanation
GIVEN:
Renee can mow a lawn in 120 MINUTES
Jeremy can mow the same lawn in 75 MINUTES
A useful approach is to assign a
"nice" value to the job.
We want a value that works well with the given information (120 minutes and 75 minutes).
600 is the least common multiple of 120 and 75
So, let's say the entire job (mowing the lawn) requires
600 STEPS
This means Renee can complete
600 steps in 120 minutes. So, Renee's RATE =
5 steps per minute
Similarly, Jeremy can complete
600 steps in 75 minutes. So, Jeremy's RATE =
8 steps per minute
So their, COMBINED rate =
5 +
8 =
13 tasks per hour
If Renee starts mowing the lawn at 2:00 P.M., and Jeremy starts helping her at 2:30 P.M., at what time will they finish mowing the lawn, rounded to the nearest minute?output = (time)(rate)
So, in the 30 minutes that Rene works ALONE, her output = (30)(5) = 150 steps.
Since the entire job consist of
600 steps, the amount of work REMAINING =
600 - 150 =
450 steps
So, working together, Renee and Jeremy need to complete the remaining
450 steps
Time = output/rate
So, time =
450/
13 ≈ 34.6 minutes
Since the two people started working TOGETHER at 2:30 pm, the time at which they have completed the job ≈ 2:30 + 34.6 minutes
≈ 3:05 pm
Answer: C
Cheers,
Brent
_________________
Brent Hanneson - founder of Greenlight Test Prep