Question

In a normal distribution 10.03% of the items are under 35kg weight and 89.97% of the items are under 80kg weight. What are the mean and standard deviation of the distribution ?

• A. mean= 47.5 and sd= 17.57
• B. mean= 47.5 and sd= 21.48
• C. mean=52.5 and sd=17.57
• D. mean=52.5 and sd=21.48

Hint:

Notice the symmetry of the percentage values: $10.03\%$ and $89.97\%$ sum to exactly $100\%$. This means the standard normal $z$-scores must be equal in magnitude and opposite in sign ($\pm z$). Thus, the mean is always the exact midpoint of the two given values.

Answer 1

The Correct Option is D