Question

There is an unusual number of accidents reported along a certain stretch of ​highway, where the speed limit is
60
60 miles per hour.

​

​The township police ​department seeks to determine if excessive speeding is a problem along that ​stretch of highway and records the speed of
30
30 cars (selected at random) ​that are using that highway.

​The table below shows the
30
30 speeds.

​



​

​Using this data, estimate the mean speed of all cars and identify the range ​of speeds within
2
2 standard deviations of the mean.


​Mean =​​
miles per hour.

​Standard deviation ≈
miles per hour.


​Lower range (+2 S.D.) = ​


Upper range (+2 S.D.) =

Answer 1

I don't see the table of the 30 speeds. Could you paste the 30 speed values here (or upload the table)? Once I have them I will compute:

- the sample mean (x̄ = sum of speeds ÷ 30),
- the sample standard deviation (s = sqrt[Σ(xi − x̄)² / (n−1)], with n = 30),
- and the 2‑SD range: lower = x̄ − 2s, upper = x̄ + 2s.

If you prefer to do it yourself, here are the steps and formulas:

1. Mean: x̄ = (x1 + x2 + … + x30)/30.
2. Sample standard deviation:
s = sqrt( [Σ(xi − x̄)²] / (30 − 1) ).
3. 2‑SD range: x̄ ± 2s.

Paste the 30 numbers and I’ll compute the numeric answers (rounded as you prefer).