6. Which one of the followings will decrease width of a confidence interval? (underline and bold the correct answer letter)
A. By increasing confidence level.
B. By increasing variability.
C. By increasing sample size.
D. By decreasing sample size.

In 2000 the average price of a football ticket was $48.28. during the next 4 years, the proce increased an average of 6% each year. a) write a model giving the average price (p), in dollars, of a ticket (t) in years after 2000.b) graph the model. estimate the year when the average ticket price was about $60