Idiot\'s Guides Basic Math and Pre-Algebra

Chapter 19: Graphs 271

Day 12 34 5 6 7 8 9 10

Time 22.71 22.68 22.50 22.43 22.37 22.19 22.04 21.97 21.91 21.89

The horizontal scale should show the day numbers, in this case up to 10, equally spaced along the
axis. The vertical scale must go high enough to record all the times, so up to about 23 seconds.
Then place a dot in line with each day’s number at a height that corresponds to that day’s time
in seconds on the vertical axis. Finally, connect the dots, day 1 to day 2 to day 3 and so on, using
straight line segments.

You may find that your first attempt is not satisfactory. If you labeled your vertical scale from 0
to 23 seconds, the graph may look very f lat. The runner’s times are only changing by a fraction
of a second at a time.

A broken scale is a good idea here. Here’s what the same graph looks like if you use a broken
scale, showing only 21.4 to 22.8 instead of 0 to 23. It’s much easier to see the changes in the
runner’s times.

20

15

10

5

0

12345678910

Times for 200 meters April 1–10

Day Number

Seconds

22.8

22.6

22.4

22.2

22

21.8

21.6

21.4

12345678910

Times for 200 meters April 1–10

Day Number

Seconds