Answer:
Step-by-step explanation:
Since the life of the brand of light bulbs is normally distributed, we would apply the the formula for normal distribution which is expressed as
z = (x - u)/s
Where
x = life of the brand of lightbulbs
u = mean life
s = standard deviation
From the information given,
u = 1300 hrs
s = 50 hrs
We want to find the probability that a light bulb of that brand lasts between 1225 hr and 1365 hr. It is expressed as
P(1225 ≤ x ≤ 1365)
For x = 1225,
z = (1225 - 1300)/50 = - 1.5
Looking at the normal distribution table, the probability corresponding to the z score is
0.06681
For x = 1365,
z = (1365 - 1300)/50 = 1.3
Looking at the normal distribution table, the probability corresponding to the z score is
0.9032
Therefore
P(1225 ≤ x ≤ 1365) = 0.9032 - 0.06681 = 0.8364
