<p>The answer is B… zzzzz haven’t we discussed this ques. before ??</p>
<p>It’s been discussed before but someone wanted to see how to use a certain formula to solve it.</p>
<p>ans = (2 * speed 1 * speed 2) / (speed 1 + speed 2)</p>
<p>The question posed by Cadillac (post 850) was “Can someone tell me how [2<em>speed1</em>speed2]/ [speed1+speed2] works? I mean obviously, I know how to plug it in, but how was this formula derived?”</p>
<p>This problem has indeed been discussed ad nauseam on CC as it continues to present a stumbling block to many students who see the problem for the time. It is good to remember that this problem usually appears at the end of a section and is considered a very hard one. When students become familiar with this site and learn the “formula” are able to solve this type of problems easily and SAVE a lot of time. </p>
<p>Unfortunately, there are always voices of discontent, especially when something is simple and elegant. Accordingly, when this problem arises, there almost someone who states that all what someone needs is work to the problem using the d=rt … formula and that students should NOT learn a formula. </p>
<p>Of course, what is missed is that working through ALL the steps of d=rt is exactly what ETS/TCB wants someone to do and waste a LOT of time or end up guessing a la PR. This is NOT necessary as this problem can easily be solved by applying the (developed) formula or using very simple REASONING. </p>
<p>In conclusion, it was NOT necessary to show how anyone could derive “Total average speed = 2 * S1*S2 / S1 +S2” from the original d=rt. </p>
<p>But someone asked :)</p>
<p>i suppose the derivation is quiet simple … Its about preferring the way we solve the problem… The “lengthy” method isn’t that long too…</p>
<p>Here we go … again! </p>
<p>Obviously, there are many different ways to solve a SAT problem. In general terms, there shouldn’t be a SAT problem that requires a lengthy mathematical manipulation. That is why some very smart people claim that every problem that appears on the SAT can be solved in 30 seconds or less. </p>
<p>As I wrote, this type of problem has a solution that requires between 10 to 15 seconds, INCLUDING reading the problem. </p>
<p>No matter how fast one is, starting with the simple standard formula will take more time. And --AGAIN-- that is exactly what ETS/TCB wants someone to do and what separates the astute and well-prepared from the others. And that is why this problem remains one that trips the majority of the students and remains at the end of a section. </p>
<p>Oh well!</p>
<p>Thanks Harambee for the example and xiggi, I understand the point you’re making. I honestly have no objections to how the equation came to be and am willing to put it to use whenever the situation arises. It’d be great if there were more “re-worked” eqns like this ;d</p>
<p>How should I approach the task of preparing for the November sat, October act, and December subject test? I’ve taken all them before so I’m familiar with the test, but how should I allocate my time to maximize output in all areas?
I’ve started my Sat prep. at the beginning of the school year, but now I’m worried whether three weeks enough is enough to prepare for the act.</p>
<p>Using all variables:
t1 + t2 = ttotal
t2 = ttotal - t1</p>
<p>d = (speed1)t1
d = (speed2)t2
(speed1)t1 = (speed2)t2
(speed1)t1 = (speed2)(ttotal) - (speed2)t1
t1(speed2 + speed1) = (speed2)(ttotal)
t1 = [(speed2)(ttotal)]/(speed1 + speed2)</p>
<p>d = (speed1)t1 = [(speed1)(speed2)(ttotal)]/(speed1 + speed2)
answer should be a round trip
2d = [2(speed1)(speed2)(ttotal)]/(speed1 + speed2)</p>
<p>This equation is for total distance traveled rather than the average speed one. It’s unnecessary, but I was bored. It might be hard to follow because my variables are confusing. When plugging in, always be sure of units as a friendly reminder too.</p>
<p>Me personally, I don’t use these formulas for rate problems since I always score extremely high on the Math anyways. I can do these problems in less than 30 seconds using the “traditional” method anyways. Saving me 15-20 certainly won’t make a difference, but if you really need the time, remembering the derived formula for average speed wouldn’t be a bad thing at all.</p>
<p>EDIT: I’m not sure if this has been mentioned yet, but now that I’m thinking about it, you could easily program this into your calculator.</p>
<p>Calculator program:
- go to prgm button
- Create new, title what ever
- Then enter this (all information can be found in catalong<2nd 0>)
: Clrhome (Instructions how to find: prgm, right once, press 8)
: Prompt a (prgm, right once, press 2)
: Disp “speed1=”, A(prgm, right once, press 3)
: Prompt b (prgm, right once, press 2)
: Disp “speed2=”, B (prgm, right once, press 3)
: (2AB)/(A+B)
: Disp Ans (prgm , right once, 3, 2nd(-))</p>
<p>Note: Prompt a can be put after disp “speed=1” and same with prompt b. It makes a little more sense this way.</p>
<p>You can do Disp (2AB)/(A+B) on the same line. That or you can set the answer to a variable such as X so you can recall it any time without having to replug in the values.</p>
<p>SAT is in a week. Any thing in particular i should do this week to enhance my score?</p>
<p>does prepping for the Psat with the Collegeboard SAT book help?</p>
<p>Yes, the blue book works for both. The difference is that the PSAT has slightly easier math and no essay.</p>
<p>I am new to this site…where do I find this 50+ pager fom xiggi</p>
<p>yea im new too i was wondering if you could show me also plx post</p>
<p>I’m not sure about the 50 pg paper you’re referring to, but there’s a summary of the xiggi method starting on post #571 of this thread.</p>
<p>Or post #1 of this thread</p>
<p>Thanks lunamom, that’s a new addition, and much easier to remember than 571 ;)!</p>
<p>Xiggi,
i am out of time for preparing for he SAT and just have 10 days in hand left.
i’m not prepared for the test near to what i should be. please recommend a book that will raise my overall score particularly that has the best tips for the essay, ways to tackle hard Math questions quickly and other strategies… PLEASE HELP!!</p>