Questions that involve the summation formula, whether on their own or one component of a more complicated problem, often trip test-takers up for the simplest of reasons: figuring out “how many items” are in the set can sometimes prove tricky. One way to avoid the headache of trying to remember the rule for each different kind of limitation (consecutive even/odd/other, inclusive vs. exclusive, whether the set starts/ends with an even/odd), is to simply employ a strategy that will quickly and consistently allow you to determine the number of items in the set: patterns.
Before we delve into how, let’s review the summation formula and when it’s used. The summation formula:
∑ = (# of Numbers in the Set)(Largest Number + Smallest Number)/2