Answer:
1/4
Explanation:
Probability is essentially (# times a specific event occurs) / (# times any general event occurs).
Here, the "specific event" is selecting a multiple of four. The multiples of 4 from 1 to 20 are: 4, 8, 12, 16, and 20 - there are 5 of these. So, the number of times the specific event can occur is 5.
The "general event" is selecting any number out of the 20. Since there are 20 numbers, then there are 20 ways that a general event occurs.
So, the probability is 5/20 = 1/4.