The excel spreadsheet has 7 boxes that should be cut out. Ask a volunteer to pick a number between 1 and 128 but they shouldn't tell you what the number is. You'll then show them each box and ask if their number is in that box or not. For any box that they say "yes" to, add the numbers that are specified at the top (1, 2, 4, 8, 16, 32, 64). Once you've gone through all 7 boxes, you'll be able to tell them what the number is.
For example, if they had chosen 99, you would have added 1 + 2 + 3