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The average of the first five multiples of 3 is:
9
3
12
15
9
For any arithmetic progression (such as multiples of a number), the average is simply the average of the first and last terms: (First + Last) / 2.
First five multiples of 3
Average=Number of observationsSum of observations
For any arithmetic progression (such as multiples of a number), the average is simply the average of the first and last terms: (First + Last) / 2.
Confusing multiples of 3 with factors of 3, or forgetting to divide the sum by 5.
Identify the Multiples
The first five multiples of 3 are obtained by multiplying 3 by 1, 2, 3, 4, and 5 respectively: 3,6,9,12,15.
3,6,9,12,15
Find the Sum
Add all five numbers together to find their total sum: 3+6+9+12+15=45.
3+6+9+12+15=45
Calculate the Average
Divide the total sum by the number of observations (n=5): Average=545=9.
Average=545=9
A is correct because the sum of the first five multiples of 3 is 45, and dividing by 5 gives an average of 9.
For any arithmetic progression, the average is always equal to the middle term when the number of terms is odd.
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