Carbon monoxide (CO) concentrations are sampled at 20 intersections in heavy-traffic areas of a city. All intersections have approximately equal daily traffic. Ten of the intersections are controlled by yield signs, and ten are controlled by stop signs. The concentrations of CO (in parts per million) are given in the table below. Because the stop signs cause more cars to travel at lower speeds, encourage periods of engine idling, and create more acceleration-deceleration phases, it is hypothesized that intersections with stop signs will have higher CO concentrations. Is this hypothesis supported at a = 0.05? [Adapted from Elementary Statistics for Geographers, Burt, Barber, and Rigby, 2009] Carbon monoxide concentration, ppm Yield Signs Stop Signs 10 31 15 16 21 17 28 22 14 27 13 11 58 12 29 18 24 20 30

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(d) Calculate the value of a test statistic: z* for Table 3, or U* for Table 13 (your choice).

(f) What conclusion do you reach about the null hypothesis? Justify.

Carbon monoxide (CO) concentrations are sampled at 20 intersections in heavy-traffic
areas of a city. All intersections have approximately equal daily traffic. Ten of the
intersections are controlled by yield signs, and ten are controlled by stop signs. The
concentrations of CO (in parts per million) are given in the table below.
Because the stop signs cause more cars to travel at lower speeds, encourage periods of
engine idling, and create more acceleration-deceleration phases, it is hypothesized that
intersections with stop signs will have higher CO concentrations. Is this hypothesis
supported at a = 0.05? [Adapted from Elementary Statistics for Geographers, Burt, Barber,
and Rigby, 2009]
Carbon monoxide concentration, ppm
Yield Signs
Stop Signs
10
31
15
16
21
17
28
22
14
27
13
11
58
12
29
18
24
20
30
Transcribed Image Text:Carbon monoxide (CO) concentrations are sampled at 20 intersections in heavy-traffic areas of a city. All intersections have approximately equal daily traffic. Ten of the intersections are controlled by yield signs, and ten are controlled by stop signs. The concentrations of CO (in parts per million) are given in the table below. Because the stop signs cause more cars to travel at lower speeds, encourage periods of engine idling, and create more acceleration-deceleration phases, it is hypothesized that intersections with stop signs will have higher CO concentrations. Is this hypothesis supported at a = 0.05? [Adapted from Elementary Statistics for Geographers, Burt, Barber, and Rigby, 2009] Carbon monoxide concentration, ppm Yield Signs Stop Signs 10 31 15 16 21 17 28 22 14 27 13 11 58 12 29 18 24 20 30
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