Question 83262

Let x=amount of time for the older machine to do the job
New machine can do (1/15) of the job per minute
The old machine can do (1/x) of the job per minute

Working together they can do (1/15)+(1/x) of the job per minute and we are told that this equals (1/12).  So our equation to solve is:

(1/15)+(1/x)=(1/12)  multiply each term by 60x to get rid of fractions

4x+60=5x  subtract 4x from both sides
4x-4x+60=5x-4x  collect like terms

x=60 minutes-----------------amount of time for the older machine to do the job

CK

(1/15)+(1/60)=(1/12)

(4/60)+(1/60)=5/60
5/60=5/60

Hope this helps----ptaylor