Stan can paint a wall in 40 minutes. if ted works together with stan, it takes both of them 1515 minutes to paint the same wall. how many minutes does it take if ted paints the wall alone?

If the wall is 100%=1, then Stan paints x percent of the wall in 15 minutes and Ted paints (1-x)=y percent of the wall in 15 minutes due to that they finish the wall in 15 minutes. Assuming Stan paints the wall at a uniform rate, he gets 15/40=3/8=0.375 of the wall done in 15 minutes, meaning that Ted paints 1-0.375=0.625 of the wall in 15 minutes. We want to know how long it takes for himself to get the wall done, so we have that if Ted finishes the wall in z minutes, 0.625/15*z=1 (since 0.625/15 is how much he gets done in 1 minute). Dividing both sides by (0.625/15), we get z=15/0.625=24