Counting as it happens, in fives
You count cars at a gate. You need a way to count as fast as they pass.
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The rule
A tally mark is one short stroke, a small straight line. You draw it when something happens.
Draw four strokes standing straight up. The fifth stroke crosses them. That closes a group of five.
Count the groups in fives. Then add the loose strokes, the strokes left over.
Counting in fives is faster than counting one by one.
Step 1 of 5
- An empty tally.
- First group of five.
- Second group of five.
- Third group of five.
- Two loose strokes. 3 groups + 2 = 17.
Check the sum: 3 × 5 = 15. Then 15 + 2 = 17.
Example
The tally has 4 groups of five and 1 loose stroke.
4 × 5 = 20 strokes. Then 20 + 1 = 21 strokes.