Please clarify

Question

I found this qn in OG. just couldnt understand the last few things...

The Water from an outlet, flowing at a constant rate, can fill a swimming pool in 9 hours. a second outlet can fill the same pool in 5 hours. how long will it take to fill the same pool if both outlet are used together.

together they can fill at the rate of 1/9+1/5= 14/45. ( i could understand this. but couldnt understand the below statements.

" thus when the outlets are used together they fill the pool in 45/14=3.21 hrs"

How is the above derived. i coulodnt understand this. am i missing out on something basic??

lunarpower · Answer

Arunlal wrote:I found this qn in OG. just couldnt understand the last few things...

The Water from an outlet, flowing at a constant rate, can fill a swimming pool in 9 hours. a second outlet can fill the same pool in 5 hours. how long will it take to fill the same pool if both outlet are used together.

together they can fill at the rate of 1/9+1/5= 14/45. ( i could understand this. but couldnt understand the below statements.

" thus when the outlets are used together they fill the pool in 45/14=3.21 hrs"

How is the above derived. i coulodnt understand this. am i missing out on something basic??

yes, it's pretty basic. it's also very important, so make sure that you learn the following somehow, whether by putting it on a flash card or by ... something:

the TIME taken to perform one job is the RECIPROCAL OF THE RATE at which that job is performed.

so, since the combined rate is 14/45, the time taken to perform one combined job is the reciprocal of that number, or 45/14.

if you want to, you could also derive this number by using a good old fashioned RTD equation: (14/45 pool/hr)(x hours) = 1 pool; therefore, x = 45/14 hour. since the right-hand side is 1 job (1 pool, in this case), you'll notice that this scenario will give you the reciprocal in all cases.

Ron has been teaching various standardized tests for 20 years.

--

Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions à Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

--

Quand on se sent bien dans un vêtement, tout peut arriver. Un bon vêtement, c'est un passeport pour le bonheur.

Yves Saint-Laurent

--

Learn more about ron

rohangupta83 · Answer

Arunlal wrote:
together they can fill at the rate of 1/9+1/5= 14/45. ( i could understand this. but couldnt understand the below statements.

the above statement means that 14 parts of the pool (out of 45 parts in total) can be filled in 1 hour.

so in 1 hour 14/45 parts can be filled

in 2 hours 2X14/45 parts = 28/45 parts can be filled

in 3 hours 42/45 parts can be filled

in 3.21 hours 45/45 parts can be filled = 1 pool

or in another way:

14/45 parts are filled in 1 hour

1 part is filled in 1 hour X 45/14

Arunlal wrote: " thus when the outlets are used together they fill the pool in 45/14=3.21 hrs"

Hope this clears things up.

Choose how you want to prepare

Get Ready for GMAT Test Day Faster with Live Online Classes

Target Test Prep EA OnDemand

Target Test Prep GMAT OnDemand

Please clarify

GMAT/MBA Expert

Re: Please clarify

Re: Please clarify

Chicago Booth

GMAT Course Reviews

Admissions Consulting Reviews

FREE GMAT PREP RESOURCES

GMAT PREP DEAL TRACKER