# QR question

#### jh311

10+ Year Member
I was just wondering if there's a general equation to do a problem that is similar to one in the Destroyer, only with a little variation. There's a question that talks about having 2 people doing the same job. one person can do the job in x number of hours and the other person can do the job in y amount of hours....so to find how much time it takes them together seems simple enough right, eqtn: xy/x+y. so multiply their times together and then divide by the sum of their times....
now, my question: What if there is a third or even a fourth person involved in the job. How do you get the time if they all work together?

#### orangutan777

##### New Member
10+ Year Member
5+ Year Member
you can use the equation 1/T1 + 1/T2 + 1/T3 = 1/total time

T1, T2, T3 for the different times.

OP
J

#### jh311

10+ Year Member
Thanks, so just for verification: Here's one that i made up and tried to see if that works. Lets say Jim can do the job in 6hrs, Bob can do it in 12, and Sally can do it in 4hrs.

1/6 + 1/12 + 1/4 = 1/Totaltime

so....
2/12 + 1/12 + 3/12 = 1/Totaltime

6/12 = 1/Totaltime

1/2 = 1/Totaltime

so Total time = 2hrs ? if they all work together right?

10+ Year Member
5+ Year Member
yep you got it