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:20%
Step-by-step explanation:216-180=36. 36/180=.20
Answer:24
Step-by-step explanation: If she bought x amount of posters and had 12 left after, you'd multiply 12 by 2 and get 24. Half of 24 is 12. So Micaela bought 24 posters.