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1. The problem statement, all variables and given/known data

The capacity of Bob's truck is 72 lbs. He needs to carry as much tar paper as possible and 1 square yard weighs 5 lbs. If the paper comes off the roll at 2 square feet per second, how long will it take to fill his truck?

2. Relevant equations

72 lbs= 5 lbs * x yd^{2}, so Bob's truck can fit 14.4 yd^{2}of tar paper.

I assume that I'm trying to find how many seconds it takes for 14.4 yd^{2}of tar paper to get in the truck.

I'll replace 72 with y,

so, the equation would be y=5x.

[itex]\frac{d}{dt}[/itex](y=5x) is [itex]\frac{dy}{dt}[/itex]=5[itex]\frac{dx}{dt}[/itex]

Anyway I know that [itex]\frac{dx}{dt}[/itex]=2ft^{2}/sec, which is .2222yd^{2}/sec when converted.

3. The attempt at a solution

I would just substitute .2222yd^{2}/sec into the derived equation to get 1.1111 lbs/sec. This means that the tar paper goes into the truck at 1.1111 lbs/sec. However, I don't know how to work this into the original equation, do I just divide 72 by 1.1111? I think I'm just being a bit stupid with this. Somebody please help this shouldn't take to long.

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# Homework Help: Related Rates Verification, Help Please

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