GMAT Math

How to solve below problem?

If 7 workers can build 7 cars in 7 days, then how many days would it take 5 workers to build 5 cars?

Thanks.

Assuming they are all working at the same rate, then 7 workers working for 7 days build cars 7 means that each worker is building 1/7 of a car a day. 5 workers working at 1/7 car a day means that they work together a 5/7 cars per day. To build 5 cars it would take;

rate * time = work

rt = w

(5/7)t= 5

t=5/(5/7)= (5/1)(7/5)=7

So it takes 5 workers 7 days to build 5 cars. Again, assuming no worker is working more efficient or less efficient than any other.

Hope that helps.

Thanks,

Jared

Wasn't sure how to calculate work per person per day. Now it makes sense.
Thanks.

sarahw_gmat wrote:How to solve below problem?

If 7 workers can build 7 cars in 7 days, then how many days would it take 5 workers to build 5 cars?

Thanks.

another way to solve this kind of problem :

think in terms of proportionality.

number of people remaining same, more work will be done if you increase the number of days they work.

Therefore, days ~ work .

similarly, if the number of days is constant, more work will be done if you increase the number of ppl working on it.

hence, number of ppl ~ work.

So, you can convert this into an equation which will be number * days = work OR n * d = w.

once you get this equation, just use (n1 * d1) / (n2* d2) = w1/ w2

for the case in hand, (7 *7)/(5 * x) = 7/5 => x = 7

quite mechanical! isn't it?

sarahw_gmat wrote:Wasn't sure how to calculate work per person per day. Now it makes sense.
Thanks.

I prefer to use my way:





Sincerely
Alberto Vidal

hephzi_bah wrote:

sarahw_gmat wrote:Wasn't sure how to calculate work per person per day. Now it makes sense.
Thanks.

I prefer to use my way:





Sincerely
Alberto Vidal

Alberto,
I am curious to know your strategy for this problem. Could you elaborate a little on this ? What is the limitation,if any, of this approach ?