7
Q:

Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:

A) 60 gallons B) 100 gallons
C) 120 gallons D) 180 gallons

Answer:   C) 120 gallons



Explanation:

Work done by the waste pipe in 1 minute ={\color{Black} \frac{1}{15}-\left ( \frac{1}{20}+\frac{1}{24} \right )=\left ( \frac{1}{15}-\frac{11}{120} \right )=-\frac{1}{40}} [-ve sign means emptying]

Volume of {\color{Black} \frac{1}{40}} part = 3 gallons

Volume of whole = (3 x 40) gallons = 120 gallons.

Q:

Water flows into a tank which is 200 m long and 150 m wide, through a pipe of cross-section (0.3m x 0.2m) at 20 km/h. In what time will the water level be 12m  ?

A) 200 hrs B) 240 hrs
C) 300 hrs D) 270 hrs
 
Answer & Explanation Answer: C) 300 hrs

Explanation:

Volume of water collected in the tank in 1 hour

⇒ (0.3 × 0.2 × 20km × 1000mts) = 1200 m cubic

If after t hours, the water is at height of 12m,

1200t=200×150×12 

⇒ t = 300 Hours.

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6 99
Q:

A Tank is normally filled in 9 hours but takes four hours longer to fill because of a leak in its bottom. If the tank is full, the leak will empty it in ?

A) 32.5 hrs B) 29.25 hrs
C) 30.30 hrs D) 31 hrs
 
Answer & Explanation Answer: B) 29.25 hrs

Explanation:

Let the leak will empty the tank in x hrs

Then,

1/9 - 1/x = 1/13

x = 29.25 hrs

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4 391
Q:

A tap can fill a tank in 6 hours. After half the tank is filled three more similar taps are opened. What is the total time taken to fill the tank completely ?

A) 4 hrs 15 min B) 3 hrs 24 min
C) 4 hrs 51 min D) 3 hrs 45 min
 
Answer & Explanation Answer: D) 3 hrs 45 min

Explanation:

Time taken by one tap to fill half of the tank = 3 hrs.

Part filled by the taps in 1 hour = 4 x 1/6 = 2/3

Remaining part = 1 - 1/2 = 1/2

2/3 : 1/2 :: 1 : p

p = 1/2 x 1 x 3/2 = 3/4 hrs. i.e., 45 min

So, total time taken = 3 hrs 45 min.

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5 532
Q:

A large tanker can be filled by two pipes A and B in 60 and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half ?

A) 31 min B) 29 min
C) 28 min D) 30 min
 
Answer & Explanation Answer: D) 30 min

Explanation:

Part filled by (A + B) in 1 minute = (1/60 + 1/40) = 1/24
Suppose the tank is filled in x minutes.
Then, x/2(1/24 + 1/40) = 1
(x/2) x (1/15) = 1 => x = 30 min.

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4 651
Q:

A tank is filled in eight hours by three pipes K, L and M. Pipe K is twice as fast as pipe L, and L is twice as fast as M. How much time will pipe L alone take to fill the tank ?

A) 32 hrs B) 24 hrs
C) 28 hrs D) 26 hrs
 
Answer & Explanation Answer: C) 28 hrs

Explanation:

1/K + 1/L + 1/M = 1/8 (Given)
Also given that K = 2L and L = 2M
=> 1/2L + 1/L + 2/L = 1/8
=> (1 + 2 + 4)/2L = 1/8
=> 2L/7 = 8
=> L = 28 hours.

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