Explanation:

- BMI is calculated as weight (in kg) divided by the square of height (in meters).

- If both weight and height increase by 10%, the new height is 1.1 times the original height, and the new weight is 1.1 times the original weight.

- The new BMI would be calculated as:

$$

\text{New BMI} = \frac{1.1 \times \text{Original Weight}}{(1.1 \times \text{Original Height})^2}

$$

- This simplifies to:

$$

\text{New BMI} = \frac{1.1 \times \text{Original Weight}}{1.21 \times (\text{Original Height})^2} = \frac{1.1}{1.21} \times \text{Original BMI}

$$

- Calculate the percentage change:

$$

\text{Percentage change} = \left(\frac{1.1}{1.21} - 1\right) \times 100\% \approx -9.09\%

$$

- Therefore, the BMI decreases by approximately 9%.

Correct Answer: Option 3, Minus 9%

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