posted by ssssss .
Xuan Yun has a total of 24 coins in her piggy bank. Some of them are twenty-cent coins and the others are fifty-cent coins. Thetotal savings is $6.90. How many twenty-cent and fifty-cent coins does she have?
number of 25 cent coins --- x
number of 50 cent coins ---- 24-x
25x + 50(24-x) = 690
solve for x and back-substitute