Page 359 - Statistics for Dummies

Chapter 21: Ten Surefire Exam Score Boosters
✓ Your professor knows that you understand the basics of the problem,
increasing your chance for partial credit. On the other hand, someone
who got the problem wrong doesn’t get much sympathy if the professor
knows drawing a simple picture would have avoided the whole problem.
✓ Students who draw pictures tend to get more problems correct than
students who don’t. Without a picture you can easily lose track of what’s
needed, and make mistakes like finding P(X < 70) instead of P(X > 70), for
example. Also, checking for and spotting errors before you turn in your
exam is easier if you have a picture to look at.
Drawing a picture may seem like a waste of valuable time on an exam, but it’s
actually a time-saver because it gets you going in the right direction, keeps
you focused throughout the problem, and helps ensure you answer the right
question. Drawing a picture can also help you analyze your final numerical
answer and either confirm you’ve got it right, or quickly a spot and fix an error
and save yourself some points. (Be sure to draw pictures while studying so
they come naturally during an exam.)
Make the Connection and 343
Solve the Problem
When you’ve figured out what the problem is asking, you have everything
labeled, and you have your pictures drawn, it’s time to solve the problem.
After doing the prep work, nine times out of ten you’ll remember a technique
you learned from class, a formula that contains the items you’ve labeled, and/
or an example you worked through. Use or remember your if-then-how chart
and you’ll be on your way. (See “Make an ‘If-Then-How’ Chart” if you need
more info.)
Breaking down a problem means having less to think about at each step, and
in a stressful exam situation where you may forget your own name, that’s a
real plus! (This strategy reminds me of the saying, “How do you eat an ele-
phant? One bite at a time.”)
In the example of using size of a home to predict its price (see the earlier sec-
tion “Label What You’re Given”), you know the mean and standard deviation
of size, the mean and standard deviation of price, and the correlation between
them; and you’ve labeled them all. The question asks you to find the equation
of the best-fitting regression line to predict price based on size of the home;
you know that means find the equation y = a + bx where x = size (square feet)
and y = price (thousands of dollars), b is the slope of the regression line, and
a is the y-intercept. (Flip to Chapter 18 for more about this formula.)

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