Using the digits 1, 2, 3, 4 and 5, with repetition allowed, how many 3-digit numbers divisible by 5 can be formed?

A number is divisible by 5 only if its units digit is 0 or 5, and only 5 is available. So the units place is fixed (1 way) while the hundreds and tens places each have all 5 digits available: $5\times 5\times 1=25$.