SOLUTION: Three computers can print out a spreadsheet for the Baldwin Accounting Firm in 12 minutes, 18 minutes, and 36 minutes. How long would it take to complete the task with all three c

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Question 24856: Three computers can print out a spreadsheet for the Baldwin Accounting Firm in 12 minutes, 18 minutes, and 36 minutes. How long would it take to complete the task with all three computers working?
An athlete begins jogging at 8mph and then at 7mph, traveling a total of 10.9 miles in 1.5 hours. How long did the athlete jog at each speed?
Found 2 solutions by Paul, stanbon:
Answer by Paul(988) (Show Source):
You can put this solution on YOUR website!
1.

6
Hence it would take them 6 minutes to complete.

2. Le x be the 8 miles times
Let y be the other time
x+y=1.5
y=1.5-x
8x+7(1.5-x)=10.9
8x-7x=10.9-10.5
x=0.4
1.5-0.4=1.1

Hence for 8mph he jogged for 0.4h and for 7mph he jogged for 1.1h.
Paul.

Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
Let number of hours the three machines run be "x" minutes.
Amount of work done by a machine is (rate)(time)
Rate of first machine is 1/12, of second is 1/18, of third is 1/36.
EQUATION:
Works done by 1st + work done by 2nd P work done by 3rd = 1 job done
(1/12)x + (1/18)x + (1/36)x = 1
3x + 2x + x = 36
6x = 36
x = 6 minutes ( time to do job if all machines are running)
Let time run at 7mph by "x" hrs.
The time run at 8mph is "1.5-x" hrs.
Formula: d=rt
Distance run at 7mph is 7x miles
Distance run at 8mph is 8(1.5-x)= 12-8x miles
EQUATION:
Dist at 7 + Dist at 8 = 10.9 miles
7x + 12-8x = 10.9
-x = -1.1
x = 1.1 (hrs. at 7mph)
1.5-x = 0.4 (hrs. at 8mph)
Cheers,
Stan H.