Question

A car is designed to last an average of 12 years with a standard deviation of 0.8 years. What is the probability that a car will last less than 10 years? (2 points)
0.621%
6.21%
93.79%
99.379%

Answer 1

Due to the common probability formula I can solve that task. Refering to the task you gave, we have all the information we need. We solve it like that: $\frac{10-12}{0.8} = -2.5; Probability(-2.5)=.0.00621; Probability = 0.621%$
So the answer is the first option 0.621%

Answer 2

Standard Deviation = A = 0.8

Mean = 12 years

We will use normal distribution to calculate probability.

Let a Random variable  Z , has A = 0.8, and M= 12 years.

Probability that a car will be able to last < 10 years= P(Z<10)

= $P[\frac{Z-M}{A}$

Pr (Z < -5/2) = 0.00621[ By using standard table]

= 0.00621 ×100

=0.621%→ Option A .