When two numbers share the middle
A sixth day adds 20 buses. Now the counts are 7, 9, 11, 12, 15 and 20. Which is the middle?
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Step 1 of 4
- Sorted: 7, 9, 11, 12, 15, 20.
- Cross off the ends: 7 and 20 go.
- Cross off the new ends: 9 and 15 go. 11 and 12 survive.
- Halfway between them: 11.5.
The middle is 11.5.
An even count of readings leaves two in the middle. The median is the number halfway between them.
Halfway between 11 and 12 is (11 + 12) ÷ 2. That is 23 ÷ 2 = 11.5.
Three readings are below 11.5 and three are above. So 11.5 is in the middle.
If the two middle readings match, the median is that number. For example, 8 and 8 give 8.