Question 1163713: Cost for copies is a linear function of the number of copies. If 100 copies cost $16.00, and 75 copies cost $13.00, write a formula for copy cost as a linear function of the number of copies. Then find how much it would cost to make 800 copies.
Answer by ikleyn(52776)   (Show Source):
You can put this solution on YOUR website! .
It is a standard linear interpolation-extrapolation formula
y =  +  .
With  = 100, = 16,  = 75,  = 13, x = 800, this prediction formula becomes
y = 16 +  = 16 + 0.12*700 = 100.00 dollars.
When the question is posed as in this post, the person "should not think".
He (or she) must know the formula (or use a textbook or handbook or his memory) and follow it literally.
The only thing the user must understand, is who are the "Xs" and who are the "Ys".
It is also useful to understand that the formula express a straight line, passing through
the points (,) and (,) in a coordinate plane.
If you don't know this formula, then memorize it (!)
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