Question

A local utility company claims that its customers' natural gas bills average less than $ 260 during the winter months of January, February, and March. A consumer group randomly selected 22 accounts for the three-month period and found the following natural gas bill amounts:

269.96

273.52

277.9

268.06

253.07

274.31

268.79

258.67

269.64

263.21

270.82

273.44

276.66

270.64

265.08

273.27

264.68

268.11

262.67

275.12

271.62

251.92

(a) Assume natural gas bills over such a period follow a normal distribution. The test statistic (z/t) is

. Use two decimals.
(b) Find the P-value in (a).

Use three decimal places.
(c) Do the data above provide statistical evidence to doubt the utility company's claim?  ? Yes No Test at α=0.07

Answer 1

Here we are using "R"

a) Test statistics:

t = 5.53

b) P-value = 1.000

c) NO