Hi, please see the homework policy for assignment related questions.
For the first question, rewording it as
generate three numbers divisible by 5 from random numbers between 100 and 500.
No three random integers are guaranteed to contain at least one occurrence of x%%5 = 0.
The second question is similar in the sense that each character might be ambiguous. Does it mean each character in the alphabet or each character in X? As to frequency, think of it as the number of a particular object in a group of objects divided by the total number of objects in the group.