Question

Two pipes A and B can fill a tank in 15 min and 20 min respectively. Both the pipes are opened together but after 4 min, pipe A is turned off. What is the total time required to fill the tank ?
A) 15 min 20 sec.
B) 16 min 40 sec.
C) 13 min 10 sec.
D) 14 min 40 sec.

Answer 1

Q:

Two pipes A and B can fill a tank in 15 min and 20 min respectively. Both the pipes are opened together but after 4 min, pipe A is turned off. What is the total time required to fill the tank ?

A) 15 min 20 sec.
B) 16 min 40 sec.
C) 13 min 10 sec.
D) 14 min 40 sec.

Answer:   D) 14 min 40 sec. 

Read Description:

Part filled in 4 minutes = 4(1/15 + 1/20) = 7/15
 
Remaining part = 1 - 7/15 = 8/15
 
Part filled by B in 1 minute = 1/20
 
1/20 : 8/15 :: 1 : k
 
k = (8/15 )x 1 x 20 = 10( 2/3) min = 10 min 40 sec.
 
The tank will be full in (4 min. + 10 min. 40 sec) = 14 min 40 sec.

Answer 2

Heyy mate ❤✌✌❤

Here's your Answer...

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Part filled in 4 minutes =4(1/15+1/20) = 7/15

Remaining part =(1-7/15) = 8/15

Part filled by B in 1 minute =1/20 : 8/15 :: 1:x 

x = (8/15*1*20) = 1023min = 10min 40sec

The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec.
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