Question

An electrical firm which manufactures certain type of bulbs wants to estimate its mean life

Answer 1

Formula:
n = [(z-value * sd)/E]^2
...where n = sample size, z-value will be found using a z-table to represent the 90% confidence interval, sd = 40, E = 10, ^2 means squared, and * means to multiply.

Plug the values into the formula and finish the calculation. Round your answer to the next highest whole number.