# A pail with 40 washers in it weighs 500 grams. The same pail with 20 washers in it weighs 420 grams. How much does the pail weigh?

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The pail is 340 grams

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Subtract 80 from both sides of the = gives

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340 grams

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We have a pail and it holds various amounts of washers. How much does the pail weigh?

The total weight for any given amount of washers is:

We know that when there are 40 washers, the pail weighs 500 grams, and so:

and we also know that when there are 20 washers the total weight is 420 grams:

To make this easier to work with, I'm going to assign the variable

We can subtract the second equation from the first - that will allow us to find

And let's substitute back in:

I'll substitute back into the other equation as well to make sure we've got this right:

That gives us the answer of:

Describe your changes (optional) 200