Answer: Python Puzzler #1385

The answer is C. The program prints:

5
10
15
20

Why?

% gives the remainder after dividing. A remainder of 0 means the number divides exactly by 5, so the program prints the multiples of 5 up to 20.

Trace table

A trace table follows the program step by step. Here’s this one:

number	number % 5	printed?
1	1
2	2
3	3
4	4
5	0	yes
6	1
7	2
8	3
9	4
10	0	yes
11	1
12	2
13	3
14	4
15	0	yes
16	1
17	2
18	3
19	4
20	0	yes

The code again

for number in range(1, 21):
    if number % 5 == 0:
        print(number)