The Percent Grid

Pre-Algebra · Axiom Academy

A hundred little squares are all you need to see what a percent really is — and how the same amount can be a percent, a fraction, and a decimal at once. "Percent" just means "out of 100" The word percent comes from per centum — "for each hundred." So a percent is nothing mysterious: it is a count out of one hundred. Here is a square cut into exactly 100 little squares. Shade some of them, and the number you shaded is the percent. Watch the grid fill in, one square at a time, up to 37 of them. Keep your eye on the three numbers as it goes: the percent counts the shaded squares, the fraction writes them over 100, and the decimal is the same value as a point-something. 37 squares shaded out of 100 is 37% — and 37/100, and 0.37. Three names, one amount. Drag the slider — or grab the handle and pull it across the grid. However many squares you shade, that is your percent: the fraction over 100 and the decimal change to match, every step of the way. Every percent is just a count of shaded squares out of 100 — read straight off the grid as a percent, a fraction, and a decimal. Some percents land on tidy pictures. Snap the slider through 10%, 25%, 50%, 75%, all the way to 100%. The fraction over 100 can often be made simpler — 25/100 is really just one quarter of the grid — but it is still the very same shaded amount. Out of 100, then made as simple as it goes: 50% is half the grid, 25% is a quarter, 20% is a fifth. Same shading, simpler fraction. One grid, three ways to say it

This is the written version of the interactive lesson above. See the full Pre-Algebra course.