Question

The life expectancy of a typical lightbulb is normally distributed with a mean of 4,000 hours and a standard deviation of 42 hours. What is the probability that a lightbulb will last between 3,875 and 4,055 hours?

a)0.8835
b)0.7825
c)0.9133
d)0.9035

Answer 1

This is the concept of statistics, to solve the question we proceed as follows;
We need to standardize our values;
z(3,875)=(3,875-4000)/42
z(3,875)=-2.9762

z(4055)=(4055-4000)/42=1.3095=1.3

Therefore;
p(3875<x<4055)
=p(-3<z<1)
=0.9034
The correct answer is D]