Question 886484
an older computer requires 15 min longer to print the payroll than does a newer computer. together the computers can print the payroll in 10 min. find the time for the new computer working alone to print the payroll.
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x=time it takes new computer working alone to print the payroll.
let 1/x=work rate of new computer
1/(x+15)=work rate of older computer
1/10=work rate working together
..
sum of indv work rates = work rate working together
{{{1/x+1/(x+15)=1/10}}}
lcd: x(x+15)
x+15+x=(x^2+15x)/10
10x+150+10x=x^2+15x
x^2-5x-150=0
solve for x by quadratic formula:
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
a=1, b=-5, c=-150
ans:
x=-3.63 (reject, x>0
or 
x=4.13
time it takes new computer working alone to print the payroll=4.13 min