Posted by Mat on Wednesday, July 30, 2014 at 6:42pm.
1.A father can do a job in a certain number of hours. His son takes twice as long to do the job. Working together, they can do the job in 6 hours. How many hours does it take the father to do the job alone?
3.David is 5 years older than Paul. In 5 years, David will be twice as old as Paul is now. How old is David now?
this is what i have so far:
2D+p(i'm not sure if this is right)
- math - bobpursley, Wednesday, July 30, 2014 at 8:47pm
combined rate=1/F +.5/F=1.5/F=1/6
subtract second equation from first
-10=-P P is 10 now, so D is 15
- math - Reiny, Wednesday, July 30, 2014 at 9:01pm
job/rate = time --> rate = job/time
let the fathers rate = job/x
let the son's rate be job/2x
combined rate =job/x + job/2x
combined time = job ÷(3job/2x)
= job (2x/3job)
but 2x/3 = 6
2x = 18
x = 9
It would take 9 hrs for the father to work alone
Paul's age --- x
David's age -- x+5
in 5 years:
David --> x+10
x+10 = 2x
x = 10
Paul is now 10 and David is now 15
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