A chorus competition was held among 20 classes in a junior high school in a school, and the order of appearance of each class was decided by drawing lots. There are 20 paper labels with the same shape

A chorus competition was held among 20 classes in a junior high school in a school, and the order of appearance of each class was decided by drawing lots. There are 20 paper labels with the same shape and size in the label box. C

* * * 20 cases, serial number is multiple of 5, including 5, 10, 15 and 20 * * *.

The probability that the serial number is a multiple of 5 is 4/20 = "1/5".

So choose C.