Tip #15 to Get a Top ACT Math Score

Charts and graphs display information, just like the sports page lists a team's wins and losses. In fact, using charts and graphs should feel no different than checking stats for your favorite Red Sox pitcher, Halo III high-scorer, or Guitar Hero hero.

The ACT uses several kinds of charts and graphs. Charts display information in rows and columns. Pie graphs represent information as part of a pie. Line graphs display how data changes, often over time. Bar graphs compare the values of several items, such as sales of different toothpastes. Pictographs use small pictures to represent data. The key to pictographs is noticing the legend. If each icon represents 8 books, then 1/2 an icon represents 4 books, not 1/2 of a book.

The key to any of these is to stay relaxed and just read the data that the chart or graph displays. Don't get intimidated. If the chart is unusual, the ACT will explain how to read it in an intro or "note." Also, we can predict most questions. Almost always the questions ask you to find the average of the data in the table, the percent that one of the categories occupies of the whole, and/or the probability of a certain piece of data occurring.

Let's look at this question:

The following chart shows the resutls when 31 high school juniors were asked to write the name of their favorite movie on a slip of paper and place it in a box.

If a slip of paper is chosen at random from the box, which of the following is closest to the percent chance that the slip chosen will name Wedding Crashers?

A. 4 % B. 13% C. 31% D. 35% E. 69%

Solution: Easy. The percent chance of choosing a slip with Wedding Crashers written on it is the number of slips that say that, divided by the total slips: , which equals 0.129 or approximately 13%.

Correct answer: B

Example Problems

The stem-and-leaf plot below shows the number of times Willy grabbed a rebound in each of 14 basketball games.

(Note: For example, 12 rebounds would have a stem value of 1 and a leaf value of 2.)

Medium

Which of the following is closest to the mean number of rebounds Willy grabbed per game?
1. 13
2. 14
3. 15
4. 16
5. 17

New Leaf Learning Center held its annual yogathon for 3 days. The total money raised in the 3 days was $24,500. The money raised, in dollars, is shown for each of the 3 days in the bar graph below.

The Sports Page: Using Charts and Graphs

Approximately what percent of the money raised by the yogathon over the 3 days did New Leaf Learning Center raise on day 2 ?
1. 12%
2. 25%
3. 33%
1. 50%
2. 65%

Answers

C Stem and leaf plots don't come up that often, but when they do, most kids are like "What the …!" That's why I included one here. If you know how to read them, they're easy. They are just a way of listing numbers. Even if you've never seen one before, the "note" tells you how to read it. The "note" tells you that the number "12" would be listed as a "1" in the first column and a "2" in the second column. So this question really is just an easy "mean" question. (Remember from Skill 4 that "mean" is just another word for "average.") So make a list of the 14 numbers, add them up, and divide by 14 to get the average.
H Many kids get scared off by a question like this because they can't get an exact number from the bar graph. That's okay, no one can. You are supposed to estimate; it's what they want you to do. So estimate the money raised on day 2. It looks a little higher than halfway between $5000 and $10,000, say $8000. Then this amount divided by the total ($24,500) gives the percent raised on day 2:

Notice that the answer choices are far enough apart that even an estimate allows us to identify the right answer.

Go to: Tip #16

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