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Dave has a collection of 47 coins. Some are $10 coins and the rest are $20 coins. If the face value is $710, how many of each denomination does he have?

 Mar 18, 2020
 #1
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Let's say all of them are $10 then the total is $470

$710 - $470 = $240

Because changing one $10 coin to a $20 coin adds $10,

There are 24 $20 coins

and 23 $10 coins

 Mar 18, 2020
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Excellent!  Solved by reasoning rather than 10X+20Y=710.  I will remember this. 

 

Thank you.

Guest Mar 18, 2020

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