Marty has a piggy bank that contains $2.25. the piggy bank contains only quarts and dimes. there are twice as many dimes as quarters. how many dimes are in the piggy bank

Let D be the number of dimes and Q be the number of quarters.

We know that the number of dimes multiplied by their value summed with the number of quarters multiplied by their value will amount to $2.25. Written mathematically:

0.10*D + 0.25*Q = 2.25

We also know that there are twice as many dimes as there are quarters, which translates to D = 2Q. So we substitute that into our previous equation:

0.10 * (2Q) + 0.25*Q = 2.25

0.20*Q + 0.25*Q = 2.25

Q = 2.25/0.45

Q = 5 quarters

Since we know that D = 2Q: D = 2 * (5) = 10 dimes