Question

Three pipes A, B and C are attached to a cistern. A and B fill it in 20 and 30 minutes respectively while C can empty it in 15 minutes. If A, B and C are kept open successively for 1 minutes each, how many minute will the cistern take to be filled.
145, 155, 173, 167

Answer 1

167 minutes

Answer 2

explain please

Answer 3

yup..

Answer 4

ok, here we go..
at first minute, pipe A will fill the cistern by 1/20 fraction
at 2nd minute, pipe B will fill by 1/30 fraction
at 3rd minute, pipe C will empty the cistern by 1/15 fraction
so, u add and subtract those fractions up, u will know, 1/60 fraction will be filled up in 3 minutes
so, it seems it will get overall 180 minutes to fill up the tank, but this is not the case. when 11/12 fractions will be filled up, the rest 1/12 fraction will be filled up by pipe A and B in 2 minutes
so, it will take total 167 minutes to fill the cistern

Answer 5

superb answer again thnks a lot dost :)