Answer: C. 12.5
Step-by-step explanation:
Given : A manufacturer of new light bulbs claims the average lifetime of its long-life bulb is more than 4000 hours.
Population mean : 
Sample size : n= 100
Sample mean : 
Standard deviation: 
The value of test-statistic is given by :-

Hence, the value of the test statistic for this problem is 12.5.
Answer:
15 - 10 = 5(3 - 2)
its 5
Step-by-step explanation: