SOLUTION: An old computer takes 6 hours longer to process the company payroll than does a new computer. If it takes the two computers 4 hours to process the payroll working together, how lon

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Question 876489: An old computer takes 6 hours longer to process the company payroll than does a new computer. If it takes the two computers 4 hours to process the payroll working together, how long does it take each take computer working alone?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
completing pay roll = 1 job
let new computer take x hours to complete the job
New computer does 1/x of the job in 1 hour
Old computer does 1/(x+6) of the job in 1 hour
Together they do 1/4 of the job in 1 hour

1/x+ 1/(x+6) =1/4
solve
%28%28x%2B6%29%2Bx%29+%2F%28x%28x%2B6%29%29=1%2F4
4%282x%2B6%29+=+x%5E2%2B6x
8x%2B24=x%5E2%2B6x
x%5E2%2B6x-8x-24=0
x%5E2-2x-24=0
x%5E2-6x%2B4x-24=0
x(x-6)+4(x-6)=0
(x-6)(x+4)=0
x=6 OR x-4
ignore negative
new computer takes 6 hours
Old takes 6+6 =12 hours