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Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today. # In detail, why did we set the width to 28.3333% -- I understand the use of percentage but not the numerical value

I understand the use of percentages for fluid but not the numerical value of 28.3333%

Hi Evan,

If you're going to have 3 columns then you first need to figure out how much the margins are taking up for 3 list items.

Each `li` has 2.5% all around. This means 2.5% on the left and on the right for a total of 5%. So each list item has 5% margin in the horizontal direction. If you're going to have 3 list items then the total margin is 3 * 5% or 15%

If the margins are taking up 15% then you have 85% left over for the widths of the list items.

85% / 3 is 28.3333% This means each list item should be 28.3333% so that it all adds up to 100%

Here's all the math written out in case it helps you understand it better.

```(2.5% + 28.3333% + 2.5%) + (2.5% + 28.3333% + 2.5%) + (2.5% + 28.3333% + 2.5%) = 100%
```

Each set of parentheses represents one list item.

Jason, thank you! That made things clear.