A pail, when holding 40 washers, weighs 500 grams. The same pail holding 20 washers weighs 420 grams. How much does the pail weigh?
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:
The pail is 340 grams
Subtract 80 from both sides of the = gives