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?

A.9

B.18

C.12

D.10

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?

A.15

B.10

C.25

D.20

this is what i have so far:

D=p+5

2D+p(i'm not sure if this is right)

- math -
**bobpursley**, Wednesday, July 30, 2014 at 8:47pm
1.

combined rate=1/F +.5/F=1.5/F=1/6

f=9 hrs

D-5=P

D+5=2P

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

= 3job/(2x)

combined time = job รท(3job/2x)

= job (2x/3job)

= 2x/3

but 2x/3 = 6

2x = 18

x = 9

It would take 9 hrs for the father to work alone

3.

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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