I've made lots of edits to this model and I now want to check that the totals are correct. And there are two glaringly empty cells right here. It's very tempting to want to just sum to the left open brackets and just start plugging away at your formula. But best practice here says if you've got a correctly done formula available to you, never recreate a formula. Just use that correct one, just drag it into the empty cells. Now that's working brilliantly. Very good. Let's just check the total costs at the bottom. Anytime you make any edits, I always worry about any unintended consequences. So let's go check on some cells that might rely on those new edits that we've made. Total cost per course. If I just click into this, let's see what's, oh dear. When we inserted those new flight rows, they were underneath the original total. There's a couple of ways we can update this. The first one is to use the visual clue. Use that blue box. Just click on that little.at the bottom right hand corner, click and drag and just bring it down. That's my favorites. An alternative is that you could click into the formula and at the moment it's going down to C51. We want it to go to C53. So what you could do, although I get very nervous doing this myself, is I could delete out the one of 51 and then type in a three for 53.

Why do I get nervous here? Because you might be in a bit of a rush. You might accidentally type in an extra number than you need. Press enterer and you've got errors. I'll press okay, and then control Z or Ctrl Zs, get rid of that. So my preference, go with the visual clues. There we go.

Now my total to the right hand side needs updating, but this time don't update this formula because you've got the correct formula to the left. Take that correct formula, drag it to the right, then you don't accidentally put in an error in the second edit here. Those totals all updated.