Mean of 3, 5, 7, 9.

**The reasoning** The mean (or average) is found by adding all numbers together, then dividing by how many numbers you have. Here's the working: - Add them up: 3 + 5 + 7 + 9 = 24 - Count how many numbers: 4 numbers - Divide: 24 ÷ 4 = **6** This is the **principle of arithmetic mean** — you're finding the "middle value" that represents all the numbers fairly. **Why the wrong options tempt you** - **Option A (5)** and **Option C (7)** are actual numbers *in* the list, so your eyes might jump to them. But mean isn't about picking from the list — it's calculated. - **Option D (8)** might come from adding incorrectly or dividing by 3 instead of 4. Always count carefully! **Quick takeaway** Mean = Sum of all values ÷ Number of values — it's *always* calculated, never just picked from the list.