A tank can be filled with water by two pipes A and B together in 36 minutes. If the pipe B was stopped after 30 minutes, the tank is filled in 40 minutes. The pipe B can alone fill the tank in:
A. 45 minutes
B. 60 minutes
C. 75 minutes
D. 90 minutes
Answer: Option D
Solution(By Examveda Team)
Let the pipes fill the tank in x minutes. Part of tank filled by pipes A and B in one minute: $$\frac{1}{{36}}$$ Part of the tank filled by pipe A in 1 minute = $$\frac{1}{{36}} - \frac{1}{x}$$ According to the question, $$\eqalign{ & 30 \times \frac{1}{{\text{x}}} + 40 \left( {\frac{1}{{36}} - \frac{1}{{\text{x}}}} \right) = 1 \cr & \Rightarrow \frac{{30}}{{\text{x}}} + \frac{{40}}{36} - \frac{{40}}{{\text{x}}} = 1 \cr & \Rightarrow \frac{{30}}{{\text{x}}} + \frac{{10}}{9} - \frac{{40}}{{\text{x}}} = 1 \cr & \Rightarrow \frac{{10}}{{\text{x}}} = \frac{1}{9} \cr} $$ Hence, x = 90 minutes.Alternatively, % of tank filled by (A+B) in 1 minute = $$\frac{{100}}{{36}}$$ = 2.78% % of tank filled in 30 minutes = 2.78 × 30 = 83% That means 17% of tank can be filled by A in last 10 minutes Then, % tank filled by A in 1 minute = $$\frac{{17}}{{10}}$$ = 1.7% % of tank filled by B in 1 minute = 2.78 - 1.7 = 1.1% So, B alone can fill 100% tank in, = $$\frac{{100}}{{1.1}}$$ = 90 minutes (approx.)
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Comments ( 4 )
Related Questions on Time and Work
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A and B together cab fill tank in 36min
(1/A)+(1/B)=1/36
(A+B)30 for 30 min A and B are filling the tank together
B stops working after 30 min
Now only A is filling tank for (40-30)=10min
30(1/36)+10(remaining tank is filled by A)=1
30/36=5/6 part of tank is filled by A and B together
1-(5/6)=1/6 part of the tank is filled by A alone in 10 min
A alone fills the whole tank in 60 min
1/60+(1/B)=1/36
1/B=1/36-(1/60)=1/90
B alone can fill the tank in 90 min
why is the answer 90 ??
when b alone can do the 1/60 work in 1 min, so he must complete the total work in 60 min??
the correct ans. Is 60 instead of 90
Plz check it twice thrice
Change your ans.
36/30= 5/6
1-5/6= 1/6
A 1/6 part done in 10 minute
1 part done in 1/6*10 = 60 minutes.
So, B alone can done in (36*60)/(60-36)= 90 minutes