The lifetime of a 2- volt non- rechargeable battery in constant use has a normal distribution with a mean of 516 hours and a standard deviation of 20 hours. What is the z-score for batteries with lifetimes of 600 hours?

Answer 1

Use z-scores.

Formula:
z = (x - mean)/sd

With your data:
z = (600 - 516)/20

I'll let you finish the calculation.