For each statement, express the null hypothesis $H_0$ and alternative hypothesis $H_1$ in symbolic form.

1.   IQ scores of statistics students have a standard deviation different from 15.

A. $H_0: \sigma = 15,$ $H_1: \sigma < 15$
B. $H_0: \sigma < 15,$ $H_1: \sigma \ge 15$
C. $H_0: \sigma \le 15,$ $H_1: \sigma > 15$
D. $H_0: \sigma = 15,$ $H_1: \sigma \not= 15$

Classify the hypothesis test as two-tailed, left-tailed or right-tailed.

A. Right-tailed
B. Left-tailed
C. Two-tailed

2.   The mean monthly bill for cell phone users has increased from the 1996 mean of 47 dollars.

A. $H_0: \mu = 47$ $H_1: \mu \not= 47$
B. $H_0: \mu \le 47,$ $H_1: \mu > 47$
C. $H_0: \mu > 47,$ $H_1: \mu < 47$
D. $H_0: \mu = 47,$ $H_1: \mu > 47$

Classify the hypothesis test as two-tailed, left-tailed or right-tailed.

A. Left-tailed
B. Two-tailed
C. Right-tailed

3.   The mean salary of statistics professors is less than 70,000 dollars.

A. $H_0: \mu = 70,000,$ $H_1: \mu < 70,000$
B. $H_0: \mu > 70,000,$ $H_1: \mu \le 70,000$
C. $H_0: \mu = 70,000,$ $H_1: \mu > 70,000$
D. $H_0: \mu < 70,000,$ $H_1: \mu \ge 70,000$

Classify the hypothesis test as two-tailed, left-tailed or right-tailed.

A. Right-tailed
B. Left-tailed
C. Two-tailed