<PRE><B>Question 1142603</B>
 Two college students have started their own business building computers from kits.
 Working alone, one student can build a computer in 20 hours.
 When the second student helps, they can build a computer in 7.5 hours.
 How long would it take the second student, working alone to build the computer?
 create and equation and solve
:
let x = the time required by the 2nd student alone
let the completed job = 1
:
Each will do a fraction of the job, the two fractions add up to 1
{{{7.5/20}}} + {{{7.5/x}}} = 1
multiply by 20x, cancel the denominators
7.5x + 20(7.5) = 20x
7.5x + 150 = 20x
150 = 20x - 7.5x
150 = 12.5x
x = 150/12.5
x = 12 hrs required by the 2nd student alone
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