<p>How do you solve problems that are like, how many consecutive numbers are trifactorable which are under 1000, or other sequence and series questions?</p>
<p>Use your brain. Look for patterns. Nobody can tell you "how to solve a problem" -- you've got to just reason it out.</p>
<p>yea but is there formulas we should know ( I know sn = n(ai +af) /2)? or do you just all count and reason for these problems</p>
<p>You find patterns. Those formulas, while great on SAT II's don't matter much on SAT I. </p>
<p>I didn't know formulas for sequences/series until long after my SAT, where I got a 780 (couldn't reason out a problem in time; nothing to do with formulas)</p>
<p>Example: look at this question: </p>
<p>* -20, -19, -18, -17 </p>
<p>The first four terms of a sequence are shown above. In the sequence, each term after the first is one more than the previous term. What is the sum of the first 50 terms? * </p>
<p>You could be a formula person and say: </p>
<p>t1 = -20
d = 1
n = 50</p>
<p>and do your little formula thing. Or you could reason it out and say: </p>
<p>* Hmm, so the first 20 terms cancel out with the 20 terms after the 21st term (zero), so all I have to do is compute the sum of the next 9 terms, which would be 21+22+23+24+25+26+27+28+29 = 225 * </p>
<p>Hence, you do not NEED formulas for SAT I questions; but you can use them if you can't reason it out quickly.</p>