Question 72718
One computer can process a payroll in 60 minutes. A newer computer can process a payroll in 40 minutes. How long would it take to process the payroll if both computers worked together?
:
Let x = time required when computers work together:
Let the completed job = 1
:
{{{x/60 + x/40}}} = 1
:
multiply equation by 120 to get rid of the denominators:
2x + 3x = 120
:
5x = 120
x = 120/5
x = 24 minutes working together
:
Check: 
24/60 + 24/40 =
2/5 + 3/5 = 1