An example of interactive technology

enhanced learning from

Sally’s Commute

Sally commutes to school and

records her commute times in whole

minutes for 70 days. The distribution

is fairly normal with mean 18 and

standard deviation 2. Can you make

her distribution? How close can you

come?

Here’s a try. We’ll start with 30 days at 18, and split

the remainder to the left and right.

After making the entries shown on the

left, we see we’ve nailed the mean at 18 but

we’re way short on the standard deviation at

1.46. It must be larger. How do we make it

closer to 2?

The distribution must be more disperse. Maybe we

can change the 30 points of value 18 to 20, and add

some more points further away from 18.

OOPS, a little too zealous.

2.22 is too large.

Some trimming is in order.

Trying to decrease the number of values further away

from 18, possibly changing the skew – that’s allowed.

Looking good. Lost the exact mean, but

we’re close. Sally rounded her commute

times anyway. I’ll take this one.

STEMLi is free visual interactivecourseware in beginning statistics

Download STEMLi at QIWCourseware.com

and try Exercise 4E4

Requires Excel 2010 for the PC Excel 2011 for the MAC

or higher

Question is:

How close can YOU come?