He is half done.
task= time*rate
time= task/rate= 1/2 / (1/40+1/60)
time= 1/2 * 120/(3+2)=60/5=12min
Mike can assemble a computer table in 40 minutes and I can do it in 60 minutes.
If Mike works for 20 minutes before I join him, how long will it take us to finish?
1 answer