Solve:

,dear student,

let the first pipe fills the reservoir in x hrs.

so according to question,

 the second pipe  fills in x-10 hrs.

so work done by first pipe in 1 hr=

and

 work done by second pipe in 1 hr=

thier work together in 1 hr=..ATQ

so,

+=

solving, we get

x=30

hope this clarifies your doubt.

regards,

team

topperlearning