Tally marks (|) and groups of five (||||/) record and count data efficiently. Tally charts organize data collected from surveys and observations in a clear, systematic way.
A tally mark is a simple scratch — one vertical line — that stands for "one thing." Every time you count something, you make one mark. This is one of the oldest ways humans have ever recorded numbers: cave dwellers, shepherds, and traders all used marks like these to keep track of things they were counting. The beauty of a tally mark is that you do not need to know how to write a number at all — you just need to make a line.
The clever twist in tally charts is what happens on the fifth mark. Instead of making a fifth vertical line, you draw one diagonal line *across* the four marks you already have, creating a bundle that looks like ||||/. This group of five is the key to making tally marks useful. Because our hands have five fingers, groups of five are easy to recognize at a glance. When you see ||||/, you instantly know "five" — you do not have to count each mark one by one. That is the whole point: tallying trades speed of recording (one quick mark at a time) for speed of reading (bundle by bundle).
To read a finished tally chart, you count the completed groups of five first, then add any leftover single marks. If you see ||||/ ||||/ ||| you know there are two fives and three more: 5 + 5 + 3 = 13. You already know how to count to 20 — your prerequisite — so this final addition step is something you can handle. A tally chart puts several of these tally columns side by side with labels, so you can compare different categories at a glance. For example, a chart tracking favorite fruits would have a row labeled "apple," a row labeled "banana," and so on, with each person's vote recorded as one tally mark in the matching row. Reading across the rows, you can instantly see which fruit got the most votes and which got the fewest — no counting, just comparing the sizes of the bundles.