Question 935751
Let x = amount of time it takes worker C alone to finish the job

Worker A works at the rate of 1/10 of the job per hour
Worker B rate is 1/12 of the job per hour
Worker C rate is 1/15 of the job per hour
In 2 hours, worker A finishes (1/10)*2=2/10 = 1/5 of the job
In 4 hours worker B finishes (1/12)*4=1/3 of the job
Together A and B have finished 1/5 + 1/3=3/15+5/15=8/15 of the job leaving 7/15 yet to be finished
So our equation to solve is:
(1/15)*x=7/15
x=7 hours
CK
(1/10)*2+(1/12)*4+(1/15)*7 should equal 1 job
Hope this helps---ptaylor