John had some ten-cent coins and some fifty-cent coins in a money box. The ratio of the number of ten-cent coins to the number of fifty-cent coins in the money box was 5:4 at first. When 20 fifty-cent coins were taken out and replaced by the same value of ten-cent coins, the...
【题目】Mike has a number of ten-cent, twenty-cent and fifty-cent coins. T he total value of all the coins is$21.60. 50% of the coins are ten-cent coins and 40% of the coins are fifty-cent coins. T he rest are twenty-cent coins. How many fifty-cent coins does Mike have?