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Donna bought a candy bar for 1.50.She paid with nickels and dimes. She used 21 coins in all. How many nickels (n) and how many dimes (d) did she use?

 Feb 11, 2021
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Okay, so this is a problem involving systems of equations. We would set up this system as follows:

 

n+d=21 (number of coins)

5n+10d=150 (amount of money)

 

For the second equation, I find it easier to remove the decimal places altogether and write it in cents instead. We can then rearrange the first equation as n=21-d and substitute that into the second. The second equation then becomes 5(21-d)+10d=150. Writing the terms out and simplifying gives us 5d=45, which becomes d=9. Therefore, we have 9 dimes. Plugging that value into the first equation gives us n=12. This means we have 12 nickels. We then double-check, and it all works out. Hopefully, this helps! - BasicMaths

 

(note: in the system of equations above, n stands for nickels and d for dimes)

 

"Mathematics is not about numbers, equations, computations, or algorithms: it is about understanding." - William Paul Thurston

 Feb 11, 2021

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