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Part VI: The Part of Tens
Now you recognize what to do — you have to find a and b. You remember (or
and
can find) that those formulas are
. Grab the numbers
you’ve labeled (
), put them
into the formulas, and solve (sounds like a commercial for a frozen dinner
and the y-intercept is
doesn’t it?). You find the slope is
, so the equation of the best-fitting regression
line is
. (See Chapter 18 for the details of regression.)
Do the Math — Twice
I can still remember some of the struggles I had way back in high school
algebra. For the longest time 3 times 2 was equal to 5 for me; this mistake
(and others like it) caused me to miss a handful of points on every exam and
homework assignment, and I just could not get past it. One day I decided I’d
had enough of losing points here and there for silly errors, and I did some-
thing about it. From that day on, I wrote out all of my work, step by step, and
resisted the urge to do steps in my head. When I got my final answer, instead
of moving on, I went back and checked every step, and I did so with the mind-
set that a mistake had probably slipped in somewhere and it was my job to
find it before anyone else did.
This approach forced me to look at each step with fresh eyes, as if I were
grading someone else’s paper. I caught more mistakes because I never
skipped over a step without bothering to check it. I finally stopped thinking
3 times 2 was 5 because I caught myself in the act enough times. My exam
grades went up, just because I started checking things more carefully. It
reminds me of the carpenter’s saying, “Measure twice, cut once.” They waste
a lot less wood that way.
Every time you find and fix a mistake before you turn in your exam, you’re get-
ting a handful of points back for yourself. Find your errors before your profes-
sor does, and you’ll be amazed how those points add up. However, remember
that time is not unlimited on an exam, so try to get the problems right the first
time. Labeling everything, drawing pictures, writing down formulas, and show-
ing all your work will definitely help!
Analyze Your Answers
A very prominent statistician I know has a framed piece of paper on his office
wall. It’s a page of an exam he took way back when he was a student. It’s got a

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