Question 164481
Let x=number of hours it takes with both working together
James stuffs at the rate of 1000/5=200 envelopes per hour
Susan stuffs at the rate of 1000/3=333.333333 =333 1/3 envelopes per hour
Together they stuff at the rate of 200+333.3333=533.3333=533 1/3  envelopes per hour
So, our equation to solve is:

(533 1/3)*x=1000  divide each side by 533 1/3
x=1.875 hours or 1 7/8 hours--------ans

Now we can stay with fractions:
x=1000/(533 1/3)=1000/(1600/3)=1000*(3/1600)=3000/1600=30/16=15/8=1 7/8 hr

Hope this helps----ptaylor