SOLUTION: please help me to solve Pencils cost 25 cents apiece. Pens cost 80 cents apiece. Susan spent $20 for a total of 36 pens and pencils. How many pencils did she buy? thank you!

Question 63629This question is from textbook An Incremental Development
: please help me to solve
Pencils cost 25 cents apiece. Pens cost 80 cents apiece. Susan spent $20 for a total of 36 pens and pencils. How many pencils did she buy?
thank you! This question is from textbook An Incremental Development

Answer by joyofmath(189) (Show Source): You can put this solution on YOUR website!
Pencils cost 25 cents apiece. Pens cost 80 cents apiece. Susan spent $20 for a total of 36 pens and pencils. How many pencils did she buy?

Let P = number of pencils.
Let E = number of pens.
Susan spent $20 dollars on 36 pens and pencils so we know:
.
We also know that Susan bought 36 things so we also know:
or .
Substitute P with 36-E in the first equation:
.
So, .
Or, .
So, or .
So, Susan bought 20 pens. She must have then bought 16 pencils since she bought 36 things altogether.
We verify these numbers by noting that 20 pens cost 20*80 = $16 and 16 pencils cost 16*.25 = $4 and the total is $20.

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