If both pipes are used together, how long will it take to fill 2/3 of the tank?

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Discussion Overview

The discussion revolves around a problem involving two inlet pipes filling a tank at different rates. Participants explore how long it will take to fill 2/3 of the tank when both pipes are used together, focusing on mathematical reasoning and problem-solving approaches.

Discussion Character

  • Mathematical reasoning, Homework-related

Main Points Raised

  • One participant sets up the problem using the rates of the two pipes, leading to the equation (1/5) + (1/3) = 1/x, and calculates x as 15/8 hours.
  • Another participant confirms the calculation and suggests multiplying the time by 2/3 to find the time to fill 2/3 of the tank.
  • A later reply presents an alternative approach, stating that if both pipes work together for 15 hours, they can fill 8 tanks, leading to the conclusion that it would take 5/4 hours to fill 2/3 of the tank.
  • Several participants express agreement with the calculations and confirm the results.
  • Some participants reflect on the challenges of solving such problems under test conditions.

Areas of Agreement / Disagreement

Participants generally agree on the calculations leading to the time required to fill 2/3 of the tank, with multiple confirmations of the results. However, there are different approaches presented, indicating a lack of consensus on the method used.

Contextual Notes

Participants do not explicitly address any assumptions or limitations in their calculations, and the discussion does not resolve any potential mathematical nuances.

Who May Find This Useful

Students preparing for tests in mathematics or physics, particularly those dealing with rates and work problems.

mathdad
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One inlet pipe fills an empty tank in 5 hours. A second inlet pipe fills the same tank in 3 hours. If both pipes are used together, how long will it take to fill 2/3 of the tank?

My Work:

Let x = time when both pipes are used together

(1/5) + (1/3) = 1/x

I found x to be 15/8 hours.

Must I now multiply (15/8)(2/3)?
 
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RTCNTC said:
I found x to be 15/8 hours.

Must I now multiply (15/8)(2/3)?
Correct.
Yes.
 
Wilmer said:
Correct.
Yes.

It took several tries before I found the correct set up. Unfortunately, no such thing as ENOUGH TIME when taking a test.
 
That's why you "practice, practice, practice" before the test!
 
Country Boy said:
That's why you "practice, practice, practice" before the test!

My classroom days ended in December 1993.
 
Then what "test" were you talking about?
 
Test tickle?
 
As a slightly different way to approach this problem, we can see that working together for 15 hours, the two inlet pipes can fill 8 tanks, and so it would take 15/8 hours for the two pipes to fill one tank, and 2/3 of that time to fill 2/3 tank, since the two pipes flow presumably at constant rates. Hence:

$$t=\frac{2}{3}\cdot\frac{15}{8}\text{ hr}=\frac{5}{4}\text{ hr}$$
 
Wilmer said:
Correct.
Yes.

(15/8)(2/3) = 5/4 hrs
 
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Stick a pink star on your forehead :)
 

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