Two pipes can independently fill a bucket in 20 minutes

Two pipes can independently fill a bucket in 20 minutes and 25 minutes. Both are opened together for 5 minutes after which the second pipe is turned off. What is the time taken by the first pipe alone to fill the remaining portion of the bucket?

On the basis of given details in question ,

Part of bucket filled by both pipes in 5 minutes = 5		1	+	1
		20		25

Part of bucket filled by both pipes in 5 minutes = 5		5 + 4		=	9
		100			20

Remaining part = 1 –	9	=	11
	20		20

This remaining part will be filled by first pipe.

∴ Required time =	11	× 20 = 11 minutes
	20