statistics
posted by Gee .
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 zscore for batteries with lifetimes of 600 hours?

Use zscores.
Formula:
z = (x  mean)/sd
With your data:
z = (600  516)/20
I'll let you finish the calculation.