Question

Energetic Co., a battery manufacturer, claims their battery lasts for 67.22 months with a standard deviation of 5.863 months. You randomly sample 35 of these batteries. Assuming the distribution for the battery lifetime is approximately normal, what is the probability the average lifetime is less than 66.14?

Question 8 options:

1)

0.5731

2)

0.8621

3)

0.4269

4)

0.1379

5)

0.2223

Answer 1

Solution :

Given that ,

mean = = 67.22

standard deviation = = 5.863

n = 35

= 67.22

= / n = 5.863 / 35 = 0.9910

P( < 66.14) = P(( - ) / < (66.14 - 67.22) / 0.9910)

= P(z < -1.0898)

= 0.1379

probability = 0.1379

Option 4) is correct