Hi All,
The GMAT is based heavily on patterns; your ability to recognize (or discover) patterns will help you to speed up and score at a higher level on Test Day. In "sequence" questions, at least one pattern will exist (the sequence has to based on a pattern; it's called a "sequence" because there's some "rule" that governs the sequence). In a prompt such as this, if you don't immediately see the pattern, then you can figure it out with a bit of experimentation.
Here, we're told to take the SUM of the positive ODD integers from 1 to N..... There's a pattern to this sequence; let's figure out what it is....
If N = 3
2 terms
1 + 3 = 4
If N = 5
3 terms
1 + 3 + 5 = 9
If N = 7
4 terms
1 + 3 + 5 + 7 = 16
Look at the sums. Do you recognize a pattern?
4....9......16......they're all PERFECT SQUARES!!!!
The next part of the question tells us the SUM of the terms in this sequence = 169 which is ALSO a perfect square (it's 13^2), so we can use this deduction along with the existing pattern we discovered to figure out the answer to the question.
169 = 13^2 = 13 terms
So we need the first 13 positive ODD integers starting with 1. We can physically list them out, if necessary...
1 3 5 7 9
11 13 15 17 19
21 23 25
Final Answer:
GMAT assassins aren't born, they're made,
Rich
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Contact Rich at: Rich.C@empowergmat.comThe Course Used By GMAT Club Moderators To Earn 750+ souvik101990 Score: 760 Q50 V42 ★★★★★ ENGRTOMBA2018 Score: 750 Q49 V44 ★★★★★