5 men can finish a job in 10 days. After 2 days 3 more men join them. For how many days they can finish a job if all of them work with the same tempo?

I guess that 5 men can do 1/5 of a job in 2 days so it remains 4/5 of a job when those 3 men join them. Hence, I supposed that question actually is "If 5 men can finish a job for 10 days, for how many days 8 men can finish 4/5 of that job?"

Is my assumption correct? How should I proceed?

Question

5 men can finish a job in 10 days. After 2 days 3 more men join them. For how many days they can finish a job if all of them work with the same tempo?

I guess that 5 men can do 1/5 of a job in 2 days so it remains 4/5 of a job when those 3 men join them. Hence, I supposed that question actually is "If 5 men can finish a job for 10 days, for how many days 8 men can finish 4/5 of that job?"

Is my assumption correct? How should I proceed?

tkhunny · Answer

That's pretty good.  You need a UNIT RATE.

1 job = 50 man-days  (5 guys and 10 days)

Then is is easy to see that

4/5 job = 40 man-days

One last thing!

gorica · Answer

ok, that means that 8 men can finish 4/5 of a job for 5 days?

tkhunny · Answer

Why do you doubt?  The Unit Rate never lies!  :-)

gorica · Answer

I just ask to be sure if I understood it :) so, 8 man, 4/5 of a job, 5 days? right?

tkhunny · Answer

40/8 = 5 -- Yup!  Division still works - woo-hoo!