Question

to fill a cistern, pipes A , B , C take 20 min ,15 min ,12 min, respectively. the time in minutes that the three pipes together will take to fill the cistern is??

Answer 1

add per minute time of all 3 pipes. The answer will be 5 minutes... hope this helps...

Answer 2

Hi friend,
If 't' is the time taken to fill the cistern by all the three pipes  then 1/t=1/t₁+1/t₂+1/t₃
t₁,t₂,t₃ are time taken by pipes A, B ,C to fill the cistern separately.
1/t=1/20+1/12+1/15
1/t=3+5+4/60
1/t=12/60
1/t=1/5
t=5min is time taken by all pipes to fill the cistern.