A room is to be painted by Jane and Sally working together. How long w

Question

Source: Nova GMAT

A room is to be painted by Jane and Sally working together. How long will it take them to paint the room together?

1. Jane can paint the room in 16 hours, working alone.
2. Sally can paint the room in 12 hours, working alone.

BrentGMATPrepNow · Answer

Target question :    How long will it take them to paint the room together?

Statement 1 : Jane can paint the room in 16 hours, working alone.   
No information about Sally's rate. 
Statement 1 is NOT SUFFICIENT

Statement 2 : Sally can paint the room in 12 hours, working alone.   
No information about Jane's rate. 
Statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined    
Statement 1 tells us Jane's rate
Statement 2 tells us Sally's rate
Since we know exactly how fast each person can paint, we COULD determine their  combined rate , which means we COULD determine  how long will it take them to paint the room together 
Of course, performing those tedious calculations on test day is a bad idea, since we need only determine whether or not the statements are sufficient. 
Since we COULD answer the  target question  with certainty, the combined statements are SUFFICIENT

Answer:  C

matthewsmith_89 · Answer

1 is insufficient because we do not know how long it would take Sally to paint the room alone
2 is insufficient because we do not know how long it would take Jane to paint the room alone
If we combine 1 & 2, sufficient

Answer is C

sasyaharry · Answer

This equation comes in handy....again 
 W=\frac{AB}{A+B}  where A and B are rates and W is the work done.

Statement 1: Gives A, nothing about B. Not sufficient
Statement 2: Gives B, nothing about A. Not sufficient

Combined: Sufficient. Answer is  C

A problem like this should take no more than 30 seconds.

ydmuley · Answer

A room is to be painted by Jane and Sally working together. How long will it take them to paint the room together?

1. Jane can paint the room in 16 hours, working alone.

As we want to find the work done by both of them together, having information on just one persons work will not be sufficient.

In this case we only Jane's time taken to complete the work but not Sally's

Hence  (1) =====> is NOT SUFFICIENT

2. Sally can paint the room in 12 hours, working alone.

Once again, as we want to find the work done by both of them together, having information on just one persons work will not be sufficient.

In this case we only know Sally's time taken to complete the work but not Jane's.

Hence  (2) =====> is NOT SUFFICIENT

Now, lets combine (1) and (2)

As you might know that, in order to find out time taken for both of them working together can be calculated by the formula

Work Done (Together) = \frac{a * b}{a + b}

Note, we need not actually solve the problem here, even knowing that we can get an answer should be sufficient.

Hence, Answer is C

gps5441 · Answer

Just to add

Combined Rate =AB/A+B)
Combined time=(A+B)/AB

This formula can only be used if individual time is given.

A room is to be painted by Jane and Sally working together. How long w

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GMAT Data Sufficiency (DS) Questions

A room is to be painted by Jane and Sally working together. How long w

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