Question

A scientist wishes to estimate the mean breaking strength of a certain type of steel rod within 3.0 psi with 95% confidence. Based on experience with a similar type of steel, she believes the standard deviation is approximately 15.0 psi in individual breaking strengths. How many steel rods should she test?

Answer 1

Answer:97 rods

Explanation:

The number of steel rods for 95% confidence level

`n=\left ( \frac{Z_(\alpha )/(2)* \hat{\sigma }}{E} \right )^2`

`Z_(\alpha )/(2)=1.96`

E=3

`\hat{\sigma }=15`

Substituting values

`n=\left ( (1.96* 15)/(3)\right )^2`

`n=96.04\approx 97`

Thus 97 rods is tested