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Algebra_4

Chapter 91

Problem 4

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Use the process of substitution to solve the following:

Given:
Pencils cost 25 cents each and
erasers cost 10 cents each.
The class bought cents worth total.
How many pencils were bought if there were more
erasers bought than pencils?

These facts can be written in shorthand form as:
25NP + 10NE = = total value in cents
and
NP + = NE = total number of erasers

Evaluate: NP = pencils


Example:

Use the process of elimination to solve the following:

Given:
There are a total of 5 nickels and dimes in a bag.
When added up, they amount to 40 cents total.
How many nickels, NN and dimes ND, are in the bag?

These facts can be written in shorthand form as:
(1) 5NN + 10ND = 40 = total cents
and
(2) NN + ND = 5 = total number of coins

Multiply equation (2) by -5 and add it to equation (1).

This gives:
5NN + 10ND = 40
-5NN - 5ND = -25
--------------------------------------
5ND = 15

(3) or ND = 3 = (number of dimes)

Substituting equation (3) back into equation (2) gives

NN + ND = NN + 3 = 5

(4) or NN = 2 = (number of nickels)