An example of interactive technology
enhanced learning from
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
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 interactive
courseware in beginning statistics
Download STEMLi at QIWCourseware.com
and try Exercise 4E4
Requires Excel 2010 for the PC
Excel 2011 for the MAC
How close can YOU come?