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A pencil at a stationery store costs $1, and a pen costs $1.50. Stella spent $21 at the store. She bought a total of 18 items. Which system of equations can be used to find the number of pencils (x) and pens (y) she bought? x + 18y = 21 x = 1.5y 18x + y = 21 x = 1.5y x + 1.5y = 21 x + y = 18 1.5x + y = 21 x = 18y

Respuesta :

Let x represent represent the amount of pencils that Stella bought, and y represent that number of pens that Stella bought.

We know that Stella bought 18 items total, meaning that the number of pencils and pens must equal 18 or :

x + y = 18

Additionally, we know that she spent $21, and that each pencil costs $1, and that each pen costs $1.50.  Therefore, 

1x + 1.5y = 21

So, the system of equations that can be used to find the number of pencils (x) and the pens (y) she bought would be:

x + 1.5y = 21
and 
x + y = 18
x+1.5y=21 because you're finding the equation you would use to find the number of pencils and pens she bought.
 Each pencil is $1 so that'd be 1x. When writing an equation, you don't write 1x, you just write x because that's all you have, 1 x. It's understood. 
Each pen is $1.50 so that would be 1.5y. 
x pencils+1.5y pens =21 dollars spent. 

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