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GMAT Consecutive Numbers

by ejkiv

July 17, 2015

GMAT consecutive numbers are those that are evenly spaced.  These are also known as arithmetic sequences, which will be discussed later, but there are so many ways in which thinking in terms of consecutive sequences can make problems easier.  A set of consecutive numbers might look like this {1, 2, 3, 4, 5} or (2, 4, 6, 8, 10} or {10, 20, 30, 40, 50} or even {14, 28, 42, 56, 70}.  There can be any amount of numbers within the set.

You may see them written as consecutive odds, in which case the set would be something along the lines of {9, 11, 13, 15...} or consecutive evens {-4, -2, 0, 2, 4, 6...}.  You may even see consecutive multiples of 5 {10, 15, 20, 25...}.  These three examples can also be written as follows:

Consecutive integers: {x, x+1, x+2, x+3...}

Consecutive odds: {x, x+2, x+4, x+6...} starting with an odd number.

Consecutive evens: {x, x+2, x+4, x+6...} starting with an even number.

Consecutive Multiples of 5: {x, x+5, x+10, x+15...}

An important thing to note is that the median (middle number) will always equal the mean (average) when working with consecutive numbers.  Although these are statistics terms, it is worth noting because this may come up in problems and it can be used to find the sum of a set of consecutive numbers.

Mean of a set of consecutive numbers: , or the middle number if the sequence has an odd number of terms.

Sum of Consecutive numbers: Mean (or Median) x the # of Terms

Let’s take a look at the sum of the numbers between 20 and 30 inclusive:

Mean = 25

# of terms = 11

Sum = 25 x 11 = 275.


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