Question 252467
Let n=time it takes for new machine to do the job.
Old does 1/(n+15) the job in 1 hr
together: 1/n + 1/(n+15)=1/6 (in one hour)
6(n+15)+6n=n(n+15) multiply each side by 6n(n+15) (LCM) to eliminate fractions.
6n+90+6n=n^2+15n
12n+90=n^2+15n
n^2+3n-90=0 subtract the left side from the right.
n=8.1 hrs. quadratic formula (below)
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Ed
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*[invoke quadratic "x", 1, 3, -90]