Sequences and series including arithmetic progression (AP) and geometric progressesion (GP) questions may appear in GMAT quant section. You could expect 1 to 2 questions covering this concept in both variants - GMAT Problem Solving (mainly as a word problem) and GMAT Data Sufficiency.
A typical series tested includes arithmetic progression and geometric or multiplicative progression. Wizako's GMAT Math Lesson Book in this chapter covers the following concepts in sequences, series, and progressions:
Here is a typical solved example in Wizako's GMAT Book from this chapter
There are 4 terms in an A.P. such that the sum of the two means is 21 and the product of the extremes is 54. What are the terms of the A.P?
A better way to represent 4 terms in AP
Let the four terms be a - 3d, a - d, a + d and a + 3d.
The sum of the two means = sum of the middle two terms
i.e., (a - d) + (a + d) = 2a = 21
or a = 10.5
The product of the two extremes = product of the first and the last term
i.e., (a - 3d)(a + 3d) = 54
a2 - 9d2 = 54
10.52 - 9d2 = 54
9d2 = 110.25 - 54 = 56.25
3d = 7.5
So, d = 2.5.
The four terms of the AP are
NoteIn the above expression, the term 'a' is not the first term as is generally the case in most AP questions and the common difference is not 'd'. There is actually no term as 'a' as part of this progression. The terms are a - 3d, a - d ... and the common difference is 2d.
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