Question 916669
Together it takes Sally and Tom 42 minutes to complete a job. Alone, Sally completes the job 13 minutes faster than Tom. How long will it take tom to complete the job alone? 
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let x=time Tom can do the job alone
1/x=Tom's work rate
x-13=time Sally can do the job alone
1/(x-13)=Sally's work rate
42=time Sally and Tom working together can finish the job
1/42=their work rate
..
indv. work rates =work rate working together
{{{1/x+1/(x-13)=1/42}}}
lcd:x(x-13)
x-13+x=x(x-13)/42
2x-13=(x^2-13x/42
84x-546=x^2-13x
x^2-97x+546=0
(x-6)(x-91)=0
x=91
time Tom can do the job alone=91 min