Remedial MathematicsSumming arithmetic series
An arithmetic series is a sequence of numbers with a fixed difference between consecutive numbers. E.g.:
2, 3, 4, 5 0, 2, 4, 6, 8, 10, 12, 14, 16, 18
Observe: The average of the first and last numbers is the average of the whole arithmetic series.
To sum an arithmetic series, multiply the length of the series by the average of the first and last numbers.