Question

How long will two pipes together take to fill a cistern which they can separetly fill in 20 minutes and 25 minutes ?​

Answer 1

Answer:

$\huge\underline\bold {Answer:}$

Part of cistern filled by 1st pipe in 1 min = 1/20

Part of cistern filled by 2nd pipe in 1 min = 1/25

Therefore part of cistern filled by both the pipes together in 1 min = 1/20 + 1/25

= 9/100

Hence the cistern will be filled by both the pipes together in 100/9 min.