Answer:
1336 phones
Explanation:
The average battery life of 2800 manufactured cell phones has a normal distribution.
The mean battery life is 14 hours, therefore: μ = 14 hours.
The standard deviation is 0.5 hours, therefore: σ = 0.5 hours.
To find the number of phones who have a battery life in the 13 to 14 range, we're going to ask for the help of a calculator. The probability of finding phones who have a battery life in the 13 to 14 range is: 0.4772. (See attached picture)
Therefore, the number of phones who have a battery life in the 13 to 14 range is: 0.4772×2800 = 1336,16 ≈ 1336 phones.