Abby has 23 coins. The coins have a total value of $\$ 4.55$. If she has only quarters (worth 25 cents each) and nickels (worth 5 cents each), how many quarters does she have?
(A) 15
(B) 17
(C) 18
(D) 16
(E) 21
If Abby had 23 nickels, the total value would be $23 \times \$ 0.05=\$ 1.15$.

But the total value of Abby's coins is $\$ 4.55$, which is $\$ 3.40$ more.

Since a quarter is worth 20 cents more than a nickel, then every time a nickel is replaced by a quarter, the total value of the coins increase by 20 cents.

For the total value to increase by $\$ 3.40$, we must replace $\$ 3.40 \div \$ 0.20=17$ nickels with quarters.

Therefore, Abby has 17 quarters.

(To check, if Abby has 17 quarters and 6 nickels, the total value of the coins that she has is $17 \times \$ 0.25+6 \times \$ 0.05=\$ 4.25+\$ 0.30=\$ 4.55$.

ANswer: (B)