Answer:
c) 50
Step-by-step explanation:
We have been given that the mean life of a particular brand of light bulb is 1200 hours. About 95% of this brand of bulbs will last between 1100 and 1300 hours.
We will use z-score formula to solve our given problem.
, where,
,
,
,
We know that 95% of data points lies within two standard deviation of mean, so 1100 will correspond to a z-score of -2 and 1300 will correspond to a z-score of 2.
We can use sample score 1300 and get same answer as:
Therefore, the standard deviation of the light bulbs’ life is 50 years.