Question 894645
2*(1-x/24) =(1-x/36)
2-x/12 = 1-x/36
2-x/12 = 1-x/36
1-x/12=-x/36
1=-x/36+x/12
1=-x/36+3x/36
1=2x/36
1=x/18 
x=18
check
Jack 2*(1-x/24) =(1-x/36) Nick
Jack 2*(1-18/24) =(1-18/36) Nick
Jack 2*(6/24) =(18/36) Nick
Jack 12/24 =18/36 Nick
Jack 1/2 =1/2 Nick
ok


check
Jack (1-x/24) (1-x/36) Nick
Jack (1-18/24) (1-18/36) Nick
Jack (1-3/4) (1-1/2) Nick
Jack (6/24) (18/36) Nick
Jack 1/4 1/2 Nick
ok
After 18 minutes Jack will have finished 3/4 and have 1/4 left 
After 18 minutes Nick will have finished  1/2 and have 1/2 left


see also http://www.algebra.com/algebra/homework/equations/Equations.faq.question.829787.html
http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Rate-of-work-word-problems.faq.question.824795.html