An automobile tire has two punctures. The first puncture by itself wou

If I had assumed 15 units,
the first puncture would have leaked \(\frac{15}{9}\) or \(\frac{5}{3}\) units in a minute
and the second puncture would have leaked \(\frac{15}{6}\) or \(\frac{5}{2}\) units in a minute

Combined they would have released \(\frac{5}{3}+\frac{5}{2} = \frac{10+15}{6} = \frac{25}{6}\) units in a minute.

The time taken to release the air by both the punctures will now be \(\frac{15 * 6}{25} = \frac{90}{25} = \frac{18}{5}\)(Option A)

The combined rate of the two punctures is:

1/9 + 1/6 = 2/18 + 3/18 = 5/18

Thus, the time to make a flat with both punctures is 1/(5/18) = 18/5 minutes.

Answer: A

Hi All,

This is an example of a "Work Formula" question - when you have two entities working together on a task, you can use the following formula to determine how long it will take the two entities to complete the task:

(A)(B)/(A+B) = time to complete the task (where A and B are the two times it takes the individuals to complete the task when working alone)

We're told that the first puncture would create a flat tire in 9 minutes and the second puncture would make a flat tire in 6 minutes. Plugging in those values, we'd have...

(9)(6)/(9+6) = 54/15 = 18/5 = 3 3/5 minutes to make a flat tire

Final Answer:

GMAT assassins aren't born, they're made,
Rich

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.