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1

<p>Is this the right way to solve this problem?</p>

<p>22222</a> - Minus.com</p>

<p>I first expanded the sequence a little bit:</p>

<p>2, -4, 8, -16, 32, -64, 128 ... </p>

<p>I noticed several things:</p>

<p>1) the even numbered terms are negative
2) the odd numbered terms were positive
3) The first 6 numbers are all <100</p>

<p>Therefore, I have to find the number of even-numbered terms from 7 to 50. </p>

<p>50 - 7 + 1 = 44 (Both endpoints are included; subtract then add 1). </p>

<p>Half of 44 = 22.</p>

<p>There are 22 even-numbered terms from 7 to 50. Those even-numbered terms are also the negative terms; the ones <100. </p>

<p>22 + 6 = 28</p>

<p>Is there a more efficient way that anyone would like to share :)?</p>

2

<p>May be simpler to consider that 1/2 of the first fifty numbers are negative, and then add the positives 2, 8, and 32. That’s 25 plus 3.</p>

3

<p>Quicker way: You should know that half will be even and half negative. So consider the number to be 25+. Now expand the sequence to get all terms <100. We see there are 6 terms below 100, and 3 of which are negative, and since we already counted the negatives we can cross them out. We are now left with 3 positive numbers >100, and 25 negatives >100. Add and you get 28.</p>

<p>Edit: too late.</p>

4

<p>Thanks guys :)!</p>