Xiggi's speed formula (average distance)

Test Preparation SAT Preparation
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<p>Can somebody explain why it works / how he came up with it? I dont want to use it without knowing why it works =&lt;/p>

<p>Xiggi’s formula can be found here:</p>

<p><a href=“http://talk.collegeconfidential.com/showthread.php?p=1040081[/url]”>http://talk.collegeconfidential.com/showthread.php?p=1040081&lt;/a&gt;&lt;/p&gt;

<p>its post #193</p>

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<p>Do you mean d=rt? he didn’t come up with that it is just a basic formula. You could explain why it works with calculus but it is easier to just think about it like this. If you drive at 50mph(that is the rate) for 2 hours(time) how far will you go? You can easily see that the formula works. Also you can rearange the formula like xiggi did to solve for variables other than d. Just trust that it works and it can help you out.</p>

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<p>you can easily get d=rt from dimensional analysis</p>

<p>but i think he’s talking about
(2xy)/(x+y)</p>

<p>It’s the harmonic mean of x and y and it gives the avg. speed of a person who goes a certain distance at x speed and then the same distance at y speed . And xiggi did not come up with harmonic mean… it has been around for a long time.</p>

<p>FYI It’s not just (x+y)/2 because the person spends more time going the slower speed</p>

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<p>LOL, have I ever said I came up with the harmonic mean formula? I merely posted about using a formula that is well beyond the scope of the SAT to solve a SAT problem in the quickest and easiest way. Despite being one of the easiest to solve, this type of problems trips the MAJORITY of the students. Anyone familiar with the formula or the way ETS poses the question in a MC should solve it without breaking a sweat. </p>

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<p>And here is an ever older quotation:</p>

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<p>As I said, keep it simple!</p>