In Grade 3 you made line plots with halves and fourths. Now the measurements go to eighths of an inch, and you can use adding and subtracting like fractions to answer questions about them.
Key idea
A line plot puts an X above a number line for each measurement. Stacks show how many times a value happened. To find the difference between the longest and shortest, subtract the values at the two ends; to combine pieces, add their values.
Why it works
Every measurement keeps its exact place on the scale, so you can read the data and still do math with it. Counting X marks tells you "how many," and the numbers under them tell you "how long."
Worked example: Difference
Using the plot, what is the difference between the longest and shortest leaf?
- Longest: $\dfrac{7}{8}$ inch. Shortest: $\dfrac{1}{8}$ inch.
- $\dfrac{7}{8} - \dfrac{1}{8} = \dfrac{6}{8}$.
Answer: $\dfrac{6}{8}$ inch
Worked example: Combine equal pieces
If all the $\dfrac{5}{8}$-inch leaves were laid end to end, how long would they be?
- There are 3 X marks above $\dfrac{5}{8}$.
- $\dfrac{5}{8} + \dfrac{5}{8} + \dfrac{5}{8} = \dfrac{15}{8} = 1\dfrac{7}{8}$.
Answer: $1\dfrac{7}{8}$ inches
Common mistake
Counting the X marks when the question asks for a length, or using the number of a stack as a measurement. Ask: does the question want "how many" (count X marks) or "how long" (use the scale values)?