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Center and spread | Lesson

What are the center and spread of a data set?

A set of quantitative data with varying values may be shown as a list or a data display.
Suppose Pedro asks 7 friends how many pairs of shoes they own. Pedro can report his findings as a list or a data display such as a dotplot where each dot represents one response.
  • List: 1, comma, 2, comma, 4, comma, 4, comma, 7, comma, 8, comma, 8
  • Dotplot:
Center and spread are ways to describe data sets like this.
  • Center describes a typical value of a data point. Two measures of center are mean and median.
  • Spread describes the variation of the data. Two measures of spread are range and standard deviation.

What skills are tested?

  • Calculating the mean, median, and range from a list of values or a data display
  • Comparing the mean, median, range, and standard deviation of data sets. You won't be tested on the formula for standard deviation.

How is the mean calculated?

The mean is useful for describing the center of data with similar values.
The mean is the average value.
start text, m, e, a, n, space, end text, equals, start fraction, start text, s, u, m, space, o, f, space, v, a, l, u, e, s, end text, divided by, start text, n, u, m, b, e, r, space, o, f, space, v, a, l, u, e, s, end text, end fraction

How is the median calculated?

The median is useful to describe the center of data with
outliers
.
The median is the middle value when the data are ordered from least to greatest.
  • If the number of values is odd, the median is the middle value.
  • If the number of values is even, the median is the average of the two middle values.

How is the range calculated?

Range measures the total spread of the data.
The range is the difference between the highest and lowest values.
start text, r, a, n, g, e, end text, equals, start text, h, i, g, h, e, s, t, space, v, a, l, u, e, end text, minus, start text, l, o, w, e, s, t, space, v, a, l, u, e, end text
A larger range indicates a greater spread in the data.

How is standard deviation used ?

Standard deviation measures the typical spread from the mean.
Standard deviation is the average distance between the mean and a data point.
Larger values of standard deviation indicate greater spread in the data.

Your turn!

TRY: FINDING THE MEDIAN
Station NumberGas Price (per gallon)
1dollar sign, 2, point, 56
2dollar sign, 2, point, 42
3dollar sign, 2, point, 65
4dollar sign, 2, point, 48
5dollar sign, 2, point, 99
Tomas visited 5 gas stations near his house. The price of gas at each station is shown in the table above. What is the median price of gas at the stations Tomas visited?
Choose 1 answer:
Choose 1 answer:

TRY: CALCULATING THE MEAN
75, comma, 70, comma, 45, comma, 50, comma, 52, comma, 68
A veterinary student is studying newborn giraffes. The list above shows the masses of 6 newborn giraffes, rounded to the nearest kilogram. What is the mean mass of the newborn giraffes?
Round you answer to the nearest kilogram.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text
kilograms

TRY: CALCULATING THE RANGE
Tayo got the following scores on her Spanish quizzes: 88, comma, 96, comma, 94, comma, 92, comma, 98, comma, 58, comma, 90. What is the range of Tayo's quiz scores?
Choose 1 answer:
Choose 1 answer:

TRY: FINDING THE MEDIAN USING A DATA DISPLAY
The dotplot above shows the volume of juice squeezed from 9 oranges. What is the median volume of juice squeezed, in fluid ounces?
Choose 1 answer:
Choose 1 answer:

Things to remember

Center describes a typical value.
  • Mean: Average value
    start text, m, e, a, n, end text, equals, start fraction, start text, s, u, m, space, o, f, space, v, a, l, u, e, s, end text, divided by, start text, n, u, m, b, e, r, space, o, f, space, v, a, l, u, e, s, end text, end fraction
  • Median: Middle value when data ordered from least to greatest
Spread describes the variation of the data.
  • Range: Total spread
start text, r, a, n, g, e, end text, equals, start text, h, i, g, h, e, s, t, space, v, a, l, u, e, end text, minus, start text, l, o, w, e, s, t, space, v, a, l, u, e, end text
  • Standard deviation: Average distance between the mean and a data point

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