Question

Add an intersection the red light times normally distributed by the mean of three minutes and a standard deviation of .25 minutes approximately what percent of red lights last between 2.5 and 3.5 minutes

Answer 1

95% of red lights last between 2.5 and 3.5 minutes.

Explanation:

In this case,

• The mean M is 3 and
• The standard deviation SD is given as 0.25

Assume the bell shaped graph of normal distribution,

The center of the graph is mean which is 3 minutes.

We move one space to the right side of mean ⇒ M + SD

⇒ 3+0.25 = 3.25 minutes.

Again we move one more space to the right of mean ⇒ M + 2SD

⇒ 3 + (0.25×2) = 3.5 minutes.

Similarly,

Move one space to the left side of mean ⇒ M - SD

⇒ 3-0.25 = 2.75 minutes.

Again we move one more space to the left of mean ⇒ M - 2SD

⇒ 3 - (0.25×2) =2.5 minutes.

The questions asks to approximately what percent of red lights last between 2.5 and 3.5 minutes.

Notice 2.5 and 3.5 fall within 2 standard deviations, and that 95% of the data is within 2 standard deviations. (Refer to bell-shaped graph)

Therefore, the percent of red lights that last between 2.5 and 3.5 minutes is 95%