Where Math Gets Real
Where Math Gets Real
Drawing a Circle Graph In “Fake News, Fake Data” you learned how to analyze graphs for accuracy. Circle graphs can be simple and accurate ways to display data es,pecially categorical data Ci.rcle graphs show how each value in a data set compares with the whole population. You can use proportional reasoning to find the size of each sector of the graph.
Where Math Gets Real
*with white behind logo EXAMPLE: A middle school includes students in Grades 5 through 8. Draw a circle graph to represent the number of students in each grade. MIDDLE SCHOOL GRA D E NUMBER O F STUDENTS Grade 5 320 Grade 6 416 Grade 7 480 Grade 8 384 TOTAL Step 1: Find the total number of students in the school. 320 + 416 + 480 + 384 = 1,600 students Where Math Gets Real Step 2: Set up a proportion for each grade. Compare these ratios: (1) the number of students in a grade to the total number of students, and (2) the number of degrees of the central angle of the sector ( x ) to the total number of degrees in a circle (360). The central angles you find should add up to 360°.
Step 3: Use cross multiplication—or another method—to solve for x in each proportion.
Grade 5:
Grade 6:
416 � 360 1,600
320 � 360 1,600
x =
= 93.6°
= 72°
x =
Grade 7:
Grade 8:
480 � 360 1,600
384 � 360 1,600
x =
= 108°
x =
= 86.4°
Step 4: Add your central angles to check that they add up to 360°.
72° + 93.6° + 108° + 86.4° = 360°
Step 5: Use a protractor to draw the appropriate- sized sectors for each grade within a circle graph, and add a title.
Step 6: The final graph should look like this:
Students in Each Grade
Grade 5:
Grade 6:
320 1,600
x 360 =
416 1,600
x 360 =
GRADE 5
GRADE 6
Grade 7:
Grade 8:
480 1,600
x 360 =
384 1,600
x 360 =
GRADE 8
GRADE 7
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Fake News, Fake Data > GRAPHING DATA, p. 1
Sessions 21 & 22 65
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