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Jason has 43 stamps. Some are worth 15 cents and some are worth 20 cents. If their total value is $7.50, how many of each kind does he have?

 Jan 24, 2020
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Jason has 43 stamps. Some are worth 15 cents and some are worth 20 cents.
If their total value is $7.50, how many of each kind does he have?

 

\(\text{Let stamps with worth $20$ cents $= x$ }\\ \text{Let stamps with worth $15$ cents $= y$ } \)

 

\(\begin{array}{|rcll|} \hline x+y &=& 43 \\ \mathbf{y} &=& \mathbf{43-x} \\ \hline \end{array}\)

 

\(\begin{array}{|rcll|} \hline 20x+15y &=& 750 \quad | \quad \mathbf{y=43-x} \\ 20x+15(43-x)&=& 750 \\ 20x+15*43-15x &=& 750 \\ 20x+645-15x &=& 750 \\ 5x +645 &=& 750 \\ 5x &=& 750 - 645 \\ 5x &=&105 \quad | \quad : 5 \\ \mathbf{x} &=& \mathbf{21} \\\\ \mathbf{y} &=& \mathbf{43-x} \\ y &=& 43-21 \\ \mathbf{y} &=& \mathbf{22} \\ \hline \end{array}\)

 

Jason does have 21 stamps with worth of 20 cents and
he does have 22 stamps with worth of 15 cents.

 

laugh

 Jan 24, 2020

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