SOLUTION: In my purse I have 21 coins, all of which are either 5-cent or 20-cent coins. Their total value is $2.25. How many 20-cent coins do I have?

Question 1046262: In my purse I have 21 coins, all of which are either 5-cent or 20-cent coins. Their total value is $2.25.
How many 20-cent coins do I have?
Answer by ikleyn(52778) (Show Source): You can put this solution on YOUR website!
.
In my purse I have 21 coins, all of which are either 5-cent or 20-cent coins. Their total value is $2.25.
How many 20-cent coins do I have?
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Let t is the number of 20-cent coins in the purse.
Then the number of the 5-cent coins is (21-t).

20-cent coins contribute 20t       cents into the total.
 5-cent coins contribute  5*(21-t) cents into the total.

The balance equation is

20t + 5*(21-t) = 225.

Simplify and solve it for t:

20t + 105 - 5t = 225,  or

20t - 5t = 225 - 105,  or

15t = 120,

t =  = 8.

Answer. There are 8 20-cent coins in the purse.

For more solved problems on coins see the lessons
    - Coin problems
    - More Coin problems
    - Solving coin problems without using equations
    - Kevin and Randy Muise have a jar containing coins
    - Typical coin problems from the archive
in this site.

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