Question

Use the relative frequency distribution in the table below to determine the following. (See Example 1 in this section.)

A Relative Frequency Distribution

Download Time (in seconds)	Percent of Subscribers
0–5	0.4
5–10	1.7
10–15	4.3
15–20	9.2
20–25	15.1
25–30	19.4
30–35	19.0
35–40	14.9
40–45	9.0
45–50	4.5
50–55	1.5
55–60	1.0

(a)

the percent of subscribers who required less than 20 s to download the file

%

(b)

the probability that a subscriber chosen at random will require at least 15 s but less than 25 s to download the file

Answer 1

A Relative Frequency Distribution

Download Time (in seconds)	Percent of Subscribers
0–5	0.4
5–10	1.7
10–15	4.3
15–20	9.2
20–25	15.1
25–30	19.4
30–35	19.0
35–40	14.9
40–45	9.0
45–50	4.5
50–55	1.5
55–60	1.0

(a)

the percent of subscribers who required less than 20 s to download the file

P[ less than 20 s to download the file ] = 0.4 + 1.7 + 4.3 + 9.2 = 15.6%

P[ less than 20 s to download the file ] = 15.6%

(b)

the probability that a subscriber chosen at random will require at least 15 s but less than 25 s to download the file

P[ 15 < X < 25 ] = 9.2 + 15.1 = 24.3

P[ 15 < X < 25 ] = 24.3