Question

Question 12 1 pts The capacities (in ampere-hours) of a particular brand of battery has a standard deviation of 14. Approximately how many batteries must be sampled so that a 99% confidence interval will specify the mean to within 2 ampere-hours (that is to say, an interval with a width of 4)? 0 326 l 133 O 1300 O 642 O 996 Question 13 1 pts Consider the following observations on maximum concrete pressure: 33.2 41.8 37.3 40.2 36.7 39.1 36.2 41.8 36.0 35.2 The normality of maximum concrete pressure was judged to be quite plausible. Calculate a 99% confidence interval for the population standard deviation of maximum pressure. O (1.78, 6.56) (3.16, 43.00) (1.91,9.45) (3.65, 89.3) O (1.38, 3.07)

Answer 1

12)

z value at 99% = 2.58

ME = 2 , s = 14

ME = z *(s/sqrt(n))
2 = 2.58 *(14/sqrt(n))
n = (2.58 *14/2)^2

n = 326

13)

From the given data , std.dev = 2.8791

n = 10

alpha = 0.01

chi square value for lower bound = 23.5894
chi square value for upper bound= 1.7349

sqrt(((10-1)* 2.8791^2)/23.5894) < sigma < sqrt(((10-1)* 2.8791^2)/1.7349)

1.78 < sigma< 6.56