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<p>it’s section 2, #19. It says that each unit on the vertical axis represents 1 foot…except there aren’t any vertical units. The only thing that could be construed as a vertical unit on the table are the has marks, but that would give you that the 3:00 level is 6 inches, which doesn’t solve the problem.</p>
<p>The answer is C</p>
<p>You know that it decreased 10% and it went down 2 at 3pm.</p>
<p>That means at 3pm the water is 20 (18/20 = 90%)</p>
<p>Thus at 4pm the water is 18 in high.</p>
<p>^ That doesn’t help at all. How did you get 18/20 or that the water was 20?</p>
<p>Here is an algebraic solution:</p>
<p>I like to use the following % change formula:</p>
<p>% change = (change/original) * 100 (multiplying by 100 simply changes the answer into a percent).</p>
<p>We are given that the % change is 10. If we let the depth at 4 PM be x, then the depth at 3 PM is x+2, and we see that the change is 2. The original is the depth at 3 PM which is x+2.</p>
<p>So substituting into the percent change formula yields:</p>
<p>10 = 2/(x+2) * 100 = 200/(x+2)</p>
<p>Cross multiply to get 10x + 20 = 200, or 10x = 180, or x = 18.</p>
<p>Now the way I would actually do it on the SAT would be by using the method of “starting with choice C.”</p>
<p>Letting choice (C) be our first guess, we see that the depth of the water at 4:00 is 18, and thus the depth at 3:00 is 20. So the change is 2, the original is 20, and the % change is (2/20)*100 = 10. Since this is correct, choice (C) is the answer.</p>
<p>Note: I used the same % change formula here as in my last post.</p>
<p>Just look at the graph. You know it went down 2 units and that had to be -10%, so it obviously started at 20. Because 20-2/20 = 100-10%</p>
<p>So just using common sense the answer is C.</p>
<p>So why do they say that each unit equals 1 foot, if each line thing actually equals 4 feet?</p>
<p>Where the hell are these vertical units anyway??? Ugh. This question epitomizes everything negative about the SAT; vague questions, misinformation, and in the end you only needed basic arithmetic.</p>
<p>theres a broken axis mark (the squiggly line near the zero). that means the graph can basically have non-equal distances from each other. therefore, in this case, zero is zero, and the next line was 16.</p>
<p>I like looking at it in terms of proportions–they simplify a lot of math.</p>
<p>If you look, the height at 3 pm is 2 units, or 2 feet higher than the height at 4 pm.
They said the decrease was 10%.</p>
<p>Therefore, 2 feet is a 10% decrease. After a 10% decrease, there is 90% left at 4 p.m.</p>
<p>2feet / x feet = 10 %/ 90%</p>
<p>Since 2 feet is 10%, we can find what 90% should be. </p>
<p>Cross multiplying that gives us:
10x = 180
x=18 ft</p>
<p>Therefore, C is the answer</p>
<p>EDIT: fail. just noticed the question had been answered already w/o confusion. my bad.</p>
<p>It turns out that the first horizontal dash after the squiggle represents 15. The squiggle itself indicates that the first dash can be starting anywhere greater than 0. There is no way to know where it starts until you finish solving the problem. Once you know that the first one is 15, it follows that the next is 16, then 17, etc. because the problem says that they are each 1 unit apart.</p>
<p>IT is C… Think about it like this. The water during 3 to 4 decreased by 10% or 2 vertical units. What # gives u 2 when u take 10% of it? That would be 20. So 20-2=18</p>
<p>The answer is C
Stop thinking about it in different ways 
Take the first horizontal dotted line as y (say)
Therefore, other lines: y+1, y+2, y+3, y+4, y+5
Depth at 3:00: y+5
Depth at 4:00: y+3
% change: 10%</p>
<p>Algebrically:
(y+5-(y+3))/(y+5)=10/100
Solve for y=15
Depth at 4:00 is y+3 = 18 feet.</p>
<p>Hope this helps.</p>