Question 85901
Q1. Kirsten does the job in 5 hours so she does {{{1/5}}} of the job per hour.
Bob does the job in 8 hours so he does {{{1/8}}} of the job per hour.
Combined they will do {{{1/8 + 1/5=13/40}}} of the job per hour. The job will therefore take{{{40/13}}}hours ie 3 hours and {{{1/13}}} of an hour or 3 hours and 4.6 minutes.
If Lisa helps the job is done in 1 hour so she must have done {{{27/40}}} of it. She would therefore take {{{40/27}}} hours or 1 hour and {{{13/40}}} of an hour or 1 hour and 19.5 minutes.

Q2. There are 17 x 7 = 119 days of painting to be done in total.
After 8 days they have painted 7 x 8 = 56 days of the job so there will be 119 - 56 = 63 days of painting to go. With a painting team of 21 painters they will take 3 days to paint the last 63 days of work.