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161

<p>Thanks again rspence!! You’ve helped a lot.</p>

162

<p>BB 2nd edition practice test 4
pg 595 #8
I’d appreciate a super-dumb down explanation as I have no idea how to solve/begin.</p>

163

<p>@rebellion510 the answer is E. Just plug in some value for a and b. I had a=60 degrees and b=70 degrees. Since all angles in a triangle will add up to 180 the top angle of the lower left triangle is 50 (180-60-70=50). Next plug in 60 for a and 70 for b in the middle triangle. Once again the top angle of that triangle is 50. The angles on a line add up to 180 degrees. So you know that the very top triangle’s lower left angle is 80 (180-50-50= 80). Plug in 70 for b in the top triangle, making c=30 degrees (180-80-70). Now look at the answer choices and plug in 60 for a and 70 for b. E is the only one that equals 30.</p>

164

<ol>
<li>A two sided coin is tossed three times. What is the probability that “heads” will be the result exactly two times?</li>
</ol>

<p>A. 3/4
B. 2/3
C. 1/2
D. 3/8
E. 1/4</p>

<p>The answer is D. I got that answer but I guessed. I would like an explanation please.</p>

165

<p>You can get the result three ways: HHT, HTH and THH.</p>

<p>Each of those three ways has (1/2)x(1/2)x(1/2)=1/8 probability. So it’s 3 times 1/8…</p>

166

<p>Thanks tranman123456, it makes sense now!</p>

167

<p>BB 2nd edition pg.610 #5 pg.613 #15
ughggh graphs…</p>

168

<ol>
<li><p>Well it asks for h(5). To get a good idea of where that will be, look at H(4) and h(6) which are about 2 and 4, respectively. Since it’s a continuous function, you can eliminate all the choices other than C(3), which is the only one in between 4 & 6.</p></li>
<li><p>First notice that it says 3 consecutive even integers. Since they give you the shortest side as x and they are consecutive & even, the sides have to x, x+2, and x+4. You know that since it’s a right triangle, x+4 is the hypotenuse. If you think of a formula relating to right triangles, you can use the Pythagorean theorem and just plug in the three values, so you get
x² + (x+2)² = (x+4)²</p></li>
</ol>

<p>If it asked you to solve for x, just multiply it out and solve.
x²+x²+4x+4 = x²+8x+16
x²-4x-12=0
(x-6)(x+2)=0
x=6
So then the triangle with the lowest value for x that fits the criteria is 6x8x10. (That part is extra but if they asked you to solve for the triangle, thats how to do it).</p>

169

<p>Hard Graphing Math Question: </p>

<p><a href=“http://img826.imageshack.us/img826/3689/8collegeconfidentialmat.pdf[/url]”>http://img826.imageshack.us/img826/3689/8collegeconfidentialmat.pdf&lt;/a&gt;&lt;/p&gt;

170

<p>f(x) = 0 when x = 1.5, 2.5, 3, 4.5 (just approximating). The function is periodic with period 5, so</p>

<p>f(1.5) = f(6.5) = f(11.5) = 0
f(2.5) = f(7.5) = 0
f(3) = f(8) = 0
f(4.5) = f(9.5) = 0</p>

<p>These are the only values of x such that 0 <= x <= 12 and f(x) = 0, so there are 9 values, B.</p>

171

<p>Barrons PSAT 2009, page 299, #10</p>

<p>If (1/a + a)^2 =144, what is the value of 1/a^2 + a^2?</p>

<p>The answer is 142. Why?</p>

172

<p>Expand (1/a + a)^2 to get</p>

<p>(1/a^2) + a^2 + 2 = 144</p>

<p>(1/a^2) + a^2 = 142</p>

173

<p>Wait, why did you add 2?
Sorry, I feel really dumb right now.</p>

174

<p>Oh, never mind, i get it now.</p>

<p>You did (1/a + a)(1/a + a).</p>

<p>Thank you!</p>

175

<p>I have another one that I solved through plugging in numbers and doing guess and check, but I want to know how to solve this the easier way.</p>

<p>If (5^a)(5^b) = 5^c/5^d, what is d in terms of a, b, and c?</p>

176

<p>Pretty simple…LHS equals 5^(a+b) and RHS equals 5^(c-d). Exponents are the same, so a+b = c-d, d = c-b-a.</p>

177

<p>Oh wow, that was so fast and simple. You just made my life a whole lot easier.</p>

178

<p>Thanks…SAT math problems tend to have a solution, and then a much faster solution. Always helps to look for the fast solution.</p>

179

<ol>
<li>The surface of a 3-dimensional solid consists of faces, each of which has the shape of a polygon. What is the least number of such faces that the solid can have?</li>
</ol>

<p>A. 2
B. 3
C. 4
D. 5
E. 6</p>

<p>The answer is …C. Please explain. I put D. Thanks in advance.</p>

180

<p>Also I am having trouble with this problem
<a href=“http://img850.imageshack.us/img850/7960/20psatoctober15sect2.jpg[/url]”>http://img850.imageshack.us/img850/7960/20psatoctober15sect2.jpg&lt;/a&gt;&lt;/p&gt;

<p>I got the right answer but I am not sure if it’s the correct way to do it. The answer is…D. I found the area of the given square then I found the area of the square the problem asks for. Then I used a ratio.</p>