Question

unstable traffic flow occurs when drivers accelerate and brake too often. unstable traffic flow wastes energy. the table below gives one example of traffic speeds, in kilometers per hour (km/h), in an unstable flow situation.

time (p.m.)	4:00	4:10	4:20	4:30	4:40	4:50	5:00
speed (km/h)	30	20	50	70	20	70	20

what is the mean speed, in km/h, in this situation?
you may use the calculator.
a. 20
b. 30
c. 40
d. 50

Explanation:

Step1: Recall mean formula

The mean $\bar{x}=\frac{\sum_{i = 1}^{n}x_{i}}{n}$, where $x_{i}$ are the data - points and $n$ is the number of data - points.

Step2: Identify data - points and number of data - points

The speeds are $x_1 = 30$, $x_2=20$, $x_3 = 50$, $x_4 = 70$, $x_5 = 20$, $x_6 = 70$, $x_7 = 20$, and $n = 7$.

Step3: Calculate the sum of data - points

$\sum_{i = 1}^{7}x_{i}=30 + 20+50 + 70+20+70+20=280$.

Step4: Calculate the mean

$\bar{x}=\frac{280}{7}=40$.

Answer:

C. 40