Question 97852
Let x=the rate at which his sister stuffs shrimp--once we know this, it will be easy to find how long it takes her to stuff 500 shrimp
 
We are told that Sam stuffs shrimp at the rate of (1000/6) shrimp per hour
We are also told that together, Sam and his sister can stuff shrimp at the rate of (1000/4) shrimp per hr.

So, (x+1000/6)=1000/4  subtract 1000/6 from both sides
x=(1000/4-1000/6)=(3000/12-2000/12)=1000/12 shrimp per hr and this of course means that she can stuff 1000 shrimp in 12 hours or 500 shrimp in 6 hours


Hope this helps---ptaylor