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?
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
Excellent! Solved by reasoning rather than 10X+20Y=710. I will remember this.
Thank you.
