kenny can assemble a desk in 40 minutes while his friend paul can assemble the same desk in 20 minutes. kenny worked for 10 minutes and decided to ask paul to work together with him to finish the job earlier, so that they can go to see a football game. how many more minutes will they need to work together to finish assembling the desk?
Kenny's rate = job/40
Paul's rate = job/20
combined rate = job/40 + job/20
= 3job/40
Kenny worked for 10 minutes, so he finished 1/4 of the job, leaving (3/4) of job to be done by both
time = (3job/4) / (3job/40)
= (3job/4)(40/(3job)) = 10 minutes
they will need another 10 minutes with both working