Tutorial on how to read and interpret histograms.
Example 1:
The histogram below shows the heights (in cm) distribution of 30 people.
a) How many people have heights between 159.5 and 169.5 cm?
b) How many people have heights less than 159.5 cm?
c) How many people have heights more than 169.5 cm?
d) What percentage of people have heights between 149.5 and 179.5 cm?
Solution to Example 1:
a) 7 people
b) 9 + 6 = 15 people
c) 5 + 2 + 1 = 8 people
d) (9 + 7 + 5)/30 = 0.7 = 70%
Example 2:
The histogram below shows the level of cholesterol (in mg per dl) of 200 people.
a) How many people have a level of cholesterol between 205 and 210 mg per dl?
b) How many people have a level of cholesterol less than 205 mg per dl?
c) What percentage of people have a level of cholesterol more than 215 mg per dl?
d) How many people have a level of cholesterol between 205 and 220 mg per dl?
Solution to Example 2:
Note that the relative frequency is shown on the vertical axis.
a) 0.2*200 = 40 people
b) (0.05 + 0.1)*200 = 30 people
c) (0.25 + 0.05) = 0.3 = 30%
d) (0.2 + 0.35 + 0.25)*200 = 160 people
Example 3:
The histogram below shows the efficiency level (in miles per gallons) of 110 cars.
a) How many cars have have an efficiency between 15 and 20 miles per gallon?
b) How many cars have have an efficiency more than 20 miles per gallon?
c) What percentage of cars have have an efficiency less than 20 miles per gallon?
Solution to Example 3:
a) 35 cars
b) 25 + 15 = 40 cars
c) (15 + 20 + 35) / 110 = 0.636 = 63.6%
More references on elementary statistics and probabilities.
