1. An island observatory has been monitoring carbon dioxide (CO₂) levelsyin the atmosphere since 1958. The table lists the average annual CO₂levels measured in parts per million (ppm) from 1990 to 2012.

Year	CO2level (ppm)
1990	354.2
1992	356.4
1994	358.8
1996	362.8
1998	366.5
2000	369.3
2002	373.4
2004	377.4
2006	381.8
2008	385.4
2010	389.8
2012	393.6

(b) Find the regression line. (Round your answers to two decimal places.)

y=

(c) Use the linear model in part (b) to estimate the CO₂level in the atmosphere in 2011. Compare your answer with the actual CO₂level of 391.6 that was measured in 2011. (Round your answer to one decimal place.)

2. Biologists have observed that the chirping rate of crickets of a certain species appears to be related to temperature. The table shows the chirping rates for various temperatures.

Temperaturet (F)	Chirping rateC (chirps/min)
50	22
55	44
60	77
65	89
70	111
75	139
80	173
85	200
90	208

(c) Use the linear model in part (b) to estimate the chirping rate at95F. (Round your answer to the nearest integer.) chirps/min

3. A certain data center monitors the amount of ice in the Arctic year round. The table gives approximate values for the sea ice extentyin millions of square kilometers from 1986 to 2012, in two-year intervals.

Year	Ice extent (million km2)	Year	Ice extent (million km2)
1986	7.5	2000	6.3
1988	7.5	2002	6.1
1990	6.1	2004	5.9
1992	7.5	2006	6.0
1994	7.2	2008	4.6
1996	8.0	2010	4.8
1998	6.5	2012	3.5

(b) Find the regression line. (Round your answers to three decimal places.)

y=

(c) Use the linear model in part (b) to estimate the ice extent in the year2014. (Round your answer to two decimal places.) million km

4. The table lists the relative abundance of mosquitoes (as measured by the mosquito positive rate) versus the flow rate (measured as a percentage of maximum flow) of canal networks in a city in Japan.

Flow rate (%),x	Mosquito positive rate (%),y
0	22
10	16
40	12
60	11
90	6
100	1

(b) Find the regression line. (Round your answers to two decimal places.)

y=

(c) Use the linear model in part (b) to estimate the mosquito positive rate if the canal flow is70%of maximum. (Round your answer to one decimal place.)

5. Audiologists study the intelligibility of spoken sentences under different noise levels. Intelligibility, the MRT scorey, is measured as the percent of a spoken sentence that the listener can decipher at a certain noise level in decibels (dB)x. The table shows the results of one such test.

Noise level (dB)	MRT score (%)
80	99
84	92
88	81
92	71
96	46
100	22
104	9

(b) Find the regression line. (Round your answers to two decimal places.)

y=

(c) Find the correlation coefficient. (Round your answer to two decimal places.)

r= Is a linear model appropriate?

Yes

No

(d) Use the linear model in part (b) to estimate the intelligibility of a sentence at a94-dB noise level. (Round your answer to two decimal places.)

6. The average life expectancy in the United Statesyhas been rising steadily over the past few decades, as shown in the table.

Year	Life expectancy
1920	54.1
1930	59.7
1940	62.9
1950	68.2
1960	69.7
1970	70.8
1980	73.7
1990	75.4
2000	76.9

(b) Find the regression line. (Round your answers to two decimal places.)

y=

(c) Use the linear model you found in part (b) to predict the life expectancy in the year2008. (Round your answer to two decimal places.) yr (d) Search the Internet or your campus library to find the actual2008average life expectancy. Compare to your answer in part (c).

7.