Pipes P and Q can fill the tank in 24 minutes and 32 minutes respectiv...
P is to be closed before 18 minutes, let it is closed after x minutes, then Q worked for all 18 minutes. So,
(1/24)*x + (1/32)*18 = 1
Solve, x = 10.5
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Pipes P and Q can fill the tank in 24 minutes and 32 minutes respectiv...
P is to be closed before 18 minutes, let it is closed after x minutes, then Q worked for all 18 minutes. So,
(1/24)*x + (1/32)*18 = 1
Solve, x = 10.5
Pipes P and Q can fill the tank in 24 minutes and 32 minutes respectiv...
Given:
- Pipe P can fill the tank in 24 minutes
- Pipe Q can fill the tank in 32 minutes
- Both pipes are opened together
- Tank needs to be full in 18 minutes
To find:
- After how many minutes the pipe P must be closed
Approach:
- Let's assume that pipe P needs to be closed after 'x' minutes
- In 'x' minutes, pipe P will fill only a fraction of the tank, and the remaining tank will be filled by both pipes working together
- We can use the formula of work, time and rate to calculate the fraction of the tank filled by pipe P in 'x' minutes
- Then, we can use the formula of work, time and rate to calculate the fraction of the tank filled in 18 minutes by both pipes working together
- Finally, we can equate these two fractions and solve for 'x'
Solution:
- Let's assume that pipe P needs to be closed after 'x' minutes
- In 'x' minutes, pipe P will fill only a fraction of the tank, and the remaining tank will be filled by both pipes working together
- Let the fraction filled by pipe P in 'x' minutes be 'p'
- According to the formula of work, time and rate, we have:
- Rate of pipe P = 1/24 (as it can fill the tank in 24 minutes)
- Work done by pipe P in 'x' minutes = (1/24) * x
- Fraction of the tank filled by pipe P in 'x' minutes = (1/24) * x / 1 = x/24 = p
- Now, let's calculate the fraction of the tank filled in 18 minutes by both pipes working together
- According to the formula of work, time and rate, we have:
- Rate of pipe P and Q working together = 1/24 + 1/32 = 8/96 + 6/96 = 14/96 = 7/48 (as they can fill the tank in 24 and 32 minutes respectively)
- Work done by both pipes in 18 minutes = (7/48) * 18
- Fraction of the tank filled by both pipes in 18 minutes = (7/48) * 18 / 1 = 7/8
- Since the tank needs to be full in 18 minutes, the fraction filled by pipe P in 'x' minutes and the fraction filled by both pipes in (18-x) minutes should add up to 1
- Therefore, we have:
- x/24 + (7/8) * (18-x) = 1
- Solving for 'x', we get:
- x/24 + 21/8 - (7/8)*x = 1
- (1/8)*x = 1/3
- x = 4
- Therefore, pipe P needs to be closed after 4 minutes, and the remaining tank will be filled by both pipes working together for the next 18-4=14 minutes
- The correct answer is option 'E' (10.5 minutes), which is the time taken by both pipes working together to fill the remaining tank (14 minutes) multiplied by the fraction of the tank filled by pipe P in 4