There are 9 numbers from 1 to 20 that are divisible by 3 or 5.
To determine this, we can list the multiples of 3 and 5 within the range of 1 to 20 and then account for any overlaps (numbers divisible by both 3 and 5).
- Multiples of 3: 3, 6, 9, 12, 15, 18 (6 numbers)
- Multiples of 5: 5, 10, 15, 20 (4 numbers)
Notice that 15 is a multiple of both 3 and 5. We've counted it twice, so we need to subtract it once to avoid overcounting.
Total numbers divisible by 3 or 5 = (Multiples of 3) + (Multiples of 5) - (Multiples of both 3 and 5) = 6 + 4 - 1 = 9.
Therefore, the numbers divisible by 3 or 5 are: 3, 5, 6, 9, 10, 12, 15, 18, and 20.
