Math questions help

Test Preparation SAT Preparation
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<p>Xiggi’s Method:
"A girl rides her bicycle to school at an average speed of 8 mph. She returns to her house using the same route at an average speed of 12 mph. If the round trip took 1 hour, how many miles is the round trip. </p>

<p>A. 8
B. 9 3/5
C. 10
D. 11 1/5
E. 12 </p>

<p>PR offers this solution: First the problem is a hard problem (level 5). TCB assumes that the common student will not attempt to solve the problem and pick the trick answer of 10 since it represents the average of 8 and 12. The common student second choice will be to pick a value that is stated in the problem: 8 or 12. PR provides the strategy to eliminate those Joe Blogg answers. Again, the conclusion of PR is to end up with two choices and pick between B and D. In their words, the student will be in great shape! </p>

<p>What’s my issue with this? In my eyes, a 50-50 chance is really not good enough. When you consider how this problem can be solved, the recommendation to guess becomes highly questionable. </p>

<p>What could a student have done? Use a simple formula for average rates -an opportunity that PR strangely forgets to mention. Is this formula really complicated? I could detail the way I developed it while working through similar problems, but the reality is that millions of people have seen it before. I’m absolutely convinced that many good tutors teach it, but you won’t find it in the typical help book. Here it is: </p>

<p>2<em>Speed1</em>Speed2] / [Speed1 + Speed2]</p>

<p>or in this case:
2* 8 * 12 / (8 + 12). </p>

<p>Most everyone will notice that the answer is 2*96/20 or simply 96/10. This yields 9.6 or 9 3/5. The total time to do this, probably 20-45 seconds. Not a bad method to know! </p>

<p>It does get better. How would I solve it? </p>

<ol>
<li>Check the problem to make sure we have a ONE hour unit. Most often, the SAT writers will use a one hour limit and not a different number of hours. </li>
<li>As soon as I verify that the unit is 1 hour, I will mark B because I know that the answer is ALWAYS a number slightly BELOW the straight average. It takes only a few problems OF THAT TYPE to realize that it ALWAYS works. </li>
<li>My total time including reading the problem: about 10 seconds!
Here you have it: two methods that are faster and are bound to yield the correct answer and a healthy dose of self-confidence!"</li>
</ol>

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<p>Total Xiggi Post. It’s posted by entomom for future reference so you don’t have to go through all 50+ pages to find the compiled list. :)</p>

<p><a href=“http://talk.collegeconfidential.com/sat-preparation/68210-xiggis-sat-prep-advice-39.html[/url]”>http://talk.collegeconfidential.com/sat-preparation/68210-xiggis-sat-prep-advice-39.html&lt;/a&gt;&lt;/p&gt;

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<p>Are you kidding me? lol
It’s not a big deal.
Distance = x
Going one way and returning makes the total distance = 2x</p>

<p>Avg. speed = total distance / total time
= 2x / (d/s + d/s) = 2x/ (x/s1 + x/s2)
Avg speed = 2/(1/s1 + 1/s2) = 2.s1.s2 / (s1+s2)
You don’t need to apply it directly most of the times. Just remember your definitions correctly and sail through like a breeze :)</p>

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<p>Thanks yall. I also missed about 5 other questions on the practice test I took, but most of those were just stupid mistakes. Any advice on how to avoid making those? ha.</p>

<p>@Zupchurch- Over the past year in my precal class whenever I’ve tried to plug in numbers I never get the right answer. So normally I don’t try that method</p>

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<p>Just practice till it becomes habit. :)</p>

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<p>Yeah, there is a large chance of error if you plug in the numbers. Like I said, there are better methods, as shown by spidey. :)</p>

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<p>I musta been on drugs when I wrote that. Wrote 5 wrong, now 7 too :o. Meant to say, the distance is the same both ways, so you should divide it by two. </p>

<p>BTW, keep your facts straight :o You used 35 instead of 30.</p>

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<p>Yeah, my bad. I deleted it all to prevent confusion.
Stupid mistake on my part, didn’t read the question fully.</p>