What is the probability that a battery lasts between 22 and 30 hours on one charge?

Apple observes that the battery in the iPhone 5 lasts for an average of 26 hours under normal
usage. Apple believes that battery life per charge is normally distributed, with a standard deviation of 5
hours.

What is the probability that a battery lasts between 22 and 30 hours on one charge?

please explain how

P(22 < T < 30) => P(T ≤ 30) - P(T ≤ 22)

so, P(z ≤ (30 - 26)/5) - P(z ≤ (22 - 26)/5)

=> P(z ≤ 0.8) - P(z ≤ -0.8)

From normal tables we get:

0.7881 - (1 - 0.7881) => 0.58:)>