To solve this problem, we need to calculate how many packs of 8 water bottles Mr. Ko needs to buy to reach or exceed 20 water bottles in total.

The division is set up as follows:

$\frac{20}{8} = 2.5$

Since 2.5 packs aren't possible (he can't buy half a pack), we need to round up to ensure Mr. Ko has enough bottles. Therefore, he needs to buy 3 packs.

So, Mr. Ko needs to buy 3 packs of water bottles to have at least 20 bottles.

Would you like more details or have any questions?

Here are some related questions for further practice:

1. If each pack had 6 bottles, how many packs would Mr. Ko need to buy?
2. What if Mr. Ko needed 25 water bottles? How many packs of 8 would he need?
3. If each pack costs $3, how much would Mr. Ko spend to buy 3 packs?
4. How many extra bottles would Mr. Ko have after buying 3 packs?
5. If each student needs 2 bottles, how many students can be served with 3 packs?

Tip: When dividing and needing a whole number, always consider if rounding up is necessary to meet requirements.