Find the standard deviation of 2,3,8,10 and 12

Analyze the question: We need the standard deviation of the data set 2, 3, 8, 10, 12.

Concept: Standard deviation (population form, as JAMB normally uses): σ = √[ Σ(x − mean)² / n ]

Step 1: Mean Sum = 2 + 3 + 8 + 10 + 12 = 35 Mean = 35 ÷ 5 = 7

Step 2: Deviations and their squares

• 2 − 7 = −5 → 25
• 3 − 7 = −4 → 16
• 8 − 7 = 1 → 1
• 10 − 7 = 3 → 9
• 12 − 7 = 5 → 25

Σ(x − mean)² = 25 + 16 + 1 + 9 + 25 = 76

Step 3: Standard deviation σ = √(76 ÷ 5) = √15.2 ≈ 3.90

(If you used the sample formula, dividing by n − 1 = 4, you'd get √19 ≈ 4.36, which is not among the options. So the intended formula is the one dividing by n.)

Answer: 3.9, which is option A.

Tip: In JAMB, unless the question says "sample", divide by n. Also, a quick check: the data spread from 2 to 12 with mean 7, and the typical deviation is around 4, so options far above that (like 5.9 or 6.9) can be eliminated fast.