Suppose that the average speed of cars on a busy section of a local highway was normally distributed with a mean of 65 mph and standard deviation of 4 mph. What is the probability that the speed of a random car in this data set was less than 53 mph? 0.025
0.0015
0.16
0.475

Explanation:

Let's convert x = 53 to its corresponding z score

z = (x-mu)/sigma

z = (53-65)/4

z = -12/4

z = -3

This indicates we're 3 standard deviations below the mean.

Recall that the Empirical Rule states that roughly 99.7% of the data items in a normal distribution are within 3 standard deviations of the mean. That leaves 100% - 99.7% = 0.3% outside this range. This small percentage is the combined percentage in both tails. Take half of this to find the amount in the left tail only.

(0.3%)/2 = 0.15%

This then converts to 0.0015 when we move the decimal point 2 spots to the left.

y = x + 95

y = 42 + 95

y=137 mm hg

- "runner b is moving at a slower rate."

- "the graphs shown are graphs of distance(km) against time(min).

the slopes of this graphs are are given by:

slope = (change in y)/(change in x)

= (change in distance)/(change in time)

this is the formula for finding the speed. so, the slope of these graphs represent the speed of the runner.

taking each division in the graph to represent 1 on both axis:

runner a ⇒ speed = (2-0)/(1-0)

= 2/1

= 2 km/min

runner b ⇒ speed = (3-0)/(3-0)

= 3/3

= 1 km/min

this shows that   runner b is moving at a slower rate."