The Σ sign: sums, limits and running totals

Read Σ with its limits, see why deviations from the mean add up to zero, use sums of products, running totals and double indices, and two shortcuts: n(n + 1)/2 and k(k − 1)/2.

Lesson 6 of 36~26 min of learningIncludes ~15 min for questions and tasks