find the sum of the first 50 numbers...

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1

<p>do these kind of problems show up frequently on the SAT math section. If so wat is the formula for finding the asnwer.</p>

2

<p>1 + 50 = 51
2 + 49 = 51
...</p>

<p>You have this for 25 pairs.</p>

<p>51 x 25 = 1275</p>

<p>I hope this is right.</p>

3

<p>^ thats correct</p>

4

<p>( 50 x 51) / 2<br>
=1275
The sum of first n numbers = n(n + 1) /2</p>

5

<p>Or you add the first number to the last number, divide by two and multiply by the number of numbers in the set.</p>

6

<p>^Thats what I learned too, but I never remember it.</p>

7

<p>thanks for the diff solutions. but do these kind of questions show up at all?</p>

8

<p>yes they do</p>

9

<p>
[quote]
Originally Posted by srk_fx
The sum of first n numbers = n(n + 1) /2

[/quote]
</p>

<p>This is only correct if the first number in the series is 1. Psycho<em>Paroxysm gave the universally correct solution (which simplifies to the one srk</em>fx gave if the first number is 1), and here it is again in symbols.</p>

<p>Sum of first n numbers: n(n + n1) /2 where n1 is the first term</p>

10

<p>"1 + 50 = 51
2 + 49 = 51
...</p>

<p>You have this for 25 pairs.</p>

<p>51 x 25 = 1275</p>

<p>I hope this is right."</p>

<p>yep thats rite</p>

11

<p>It just depends.</p>

<p>I think that formula is faster.</p>

<p>The way I did it is the only method I saw right away.</p>

<p>It's always good to find out the best method to solve a certain problem so you can save time.</p>

12

<p>My bad.My formula is only true if a sequence begins with one.</p>

<p>But after I take a deep look at the problem,it is unsolvable since it dosen't state the beginning of the series.The sum of first 50 numbers beginning with what? To solve an arithmetic series you have to know the first term .Skatearabia's formula is the correct one.</p>

13

<p>
[quote]
find the sum of the first 50 numbers...

[/quote]

Aren't negatives numbers too? An alternative would be to use your calculator and type everything in one by one.</p>

14

<p>
[quote]
An alternative would be to use your calculator and type everything in one by one.

[/quote]
</p>

<p>Thats VERY time consuming , especialy on the SAT and especially since your doing like 50 numbers...it d be easier just to skip the question..........</p>

15

<p>Oh. I gave the wrong, or at least a misleading, formula. Sorry.</p>

<p>Sum of first n numbers in an arithmetic series = n(aN + a1) /2</p>

<p>where aN = nth term, and a1 = 1st term</p>

16

<p>SCOORREE for the Psycho! :)
By the way I learned this a long time ago from this book called Shortcut Math. I forgot who the author was, but it's this small little blue paperback book. It's somewhere in my shelf...
Very helpful book. :)</p>

17

<p>You should also memorize the formula for the sum of a finite or infinte geometric series (if not for the SAT I then for the SAT II).</p>