Question

The lifetime of a 2- volt non-rechargeable battery in constant use has a normal distribution of 516 hours and a standard deviation of 20 hours. What is the z- score for batteries with lifetimes of 520 hours?

Answer 1

Use z-scores.

Formula:
z = (x - mean)/sd

With your data:
z = (520 - 516)/20

I'll let you finish the calculation.

Answer 2

0.2