Math CentralQuandaries & Queries


Question from Kelsey, a student:

_, 2, _, _, 250, _

i don't know how to fill in the missing terms

Hi Kelsey,

You identified this as a geometric sequence so there is a number r, called the common ratio, so that each term after the first is r time the previous term. You know the second term is 2 so the third term is 2 × r. Now that you know the second term you know that the third term is (2 × r) × r = 2 × r2. What is the fourth term? You know fourth term is 125 so what is r?


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