Answer:
Step-by-step explanation:
Since the life span of the battery pack is known to be Normally distributed, we would apply the formula for normal distribution which is expressed as
z = (x - µ)/σ
Where
x = life spans of battery packs.
µ = mean life span
σ = standard deviation
From the information given,
µ = 250 hours
σ = 20 hours
The probability that a battery pack lasts longer than 260 hours. It is expressed as
P(x > 260) = 1 - P(x ≤ 260)
For x = 260
z = (260 - 250)/20 = 0.5
Looking at the normal distribution table, the probability corresponding to the z score is 0.69
The percentage of battery packs that lasts longer than 260 hours is
0.69 × 100 = 69%
