Hmm

I'll probably do it exactly the same as Chris, I just want to play with it.  :)

4 people take 2.5 hours to do 1/2 the job

so

4 people will take 5 hours to do the whole job

so

1 person will take 20 hours to do the whole job

so

10 people will take 2 hours to do the whole job

so

10 people will take 2/3 hours to do 1/3 of the job

2/3 of an hour is 40 minutes.     So it will take 10 people 40minutes to do 1/3 of the job.     Ta~da

Hmm. For some reason, I got 1000. O_O

in 1000  they can build a building

Yes you are right, 40 minutes is what I've got.

Oh! My bad! The picture is blocked, So I cannot see it. :(

Why ? did you wanna i can send you link to the photo ?

For some reason, Any pictures on here are blocked, But when I get home, they are not..

http://s019.radikal.ru/i643/1601/03/69b71acc291c.jpg

4 people finish 1/2 of a job in 2 1/2 hours,

therefore the 4 people will finish the job in 5 hours, or 300 minutes.

10 people will finish same job in 4/10 X 300=120 minutes, therefore,

1/3 of the job will be finished in:

1/3 X 120=40 minutes.

yea i did the same

If 4 people can do 1/2 the job in 2hr, 30 min [ 150 min], then it must take them 300 min to do the whole job.

And  we can use the "see- saw" principle, here.

4 * 300  = 10 * (time to do the same job)  ....    divide both sides by 10

4*300/ 10   = 120 minutes to do the whole job  for a crew of 10 people

Then, 1/3 of the job will take a crew of 10 people  40 minutes to complete

4 people take 2.5 hours to do 1/2 the job

people 4-10  4*5/2=10       job 1/2-1/3 1/2*2/3=1/3

10 people take x hours to do 1/3 the job

 so: (150*2*2)/(3*5)=40

i did the same :P :D