Question

Two pipes can fill a cistern 20 minutes and 30 minitues respectively.both pipes being opened.time when the first pipes must be turned off.so the cistern may be filled in 10 minutes more will be​

Answer 1

Answer:

the cistern filling in 20 mins be A and the other be B

In 1 min a fills 1/20 B fills 1/30

so when opened together they fill 1/20+1/30

they fill 1/12 in 1 min

In 10 mins B fills 1/30x10= 1/3

so left is 2/3 to b filled @ 1/12 per min

so time taken is 2/3 devided by 1/12 = after 8 mins A should b off