Find the mean of: 12, 15, 18, 20, 25.

**The reasoning** The **mean** (or average) is the sum of all values divided by how many values you have. Here's the working: - Add all the numbers: 12 + 15 + 18 + 20 + 25 = 90 - Count how many numbers: 5 numbers - Divide: Mean = 90 ÷ 5 = **18** This is the **principle of arithmetic mean** — you're finding the central value that would result if you distributed the total equally. **Why the wrong options tempt you** - **17** might catch you if you miscounted the total or divided by 6 instead of 5 - **19** could come from adding incorrectly (maybe getting 95 instead of 90) - **20** is tempting because it's the middle number when you arrange them in order (that's the *median*, not the mean!) Students often confuse mean with median — don't fall for it! **Quick takeaway** Mean = Add everything up, then divide by how many items you counted — it's about fair sharing, not middle position.