Question

Mr Yang’s son has a total of twenty-one $1 and $2 coins in his money box. When he counts his money, he finds that its total value is $30. How many coins of each type does he have?

Answer 1

Hello!

To solve this, first assume all the coins are $1. Then, find the value that would have. 1 * 21 = $21.

Now, see how far away from $30 we are. 30 - 21 = 9. Therefore, we need an increase by $9.

For each coin changed from a $1 to a $2, how much of an increase is there? $1. Therefore, change 9 coins to $2 coins to have an increase of $9. If he has 9 $2 coins, he'll have 21 - 9 $1 coins, or 12.

Therefore, your final answer is 12 $1 coins and 9 $2 coins.

Hope this helps!