challenging math questions

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^answer is 4! right? 24 combinations? </p>

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<p>I know it's a lot, but I really need help on these ones, so if any one could help, I would appreciate it SO much!</p>

<p>help please!! i’m taking my sat this saturday :(</p>

<p>I’ll go top to bottom</p>

<p>1) Just know that all the expressions are supposed to be integers in consecutive order, after that, it’s all about plugging in your own numbers.</p>

<p>So, say we want the order to be 1, 2, 3, 4 (we won’t even need the 4, because by the 3rd expression we should be able to do w * y, and we’ll even have x). Plug in some random numbers for v and w to make them equal to 4 so that we can do 4/4 for it to equal 1. Let’s choose v = 1, w = 3. Simple. Now, for the next one. Make w + x, aka 3 + x should equal to 8 so we can divide it by 4 to get 2 (still remember, we do this because of consecutive order). Obviously, x is 5. Now, for the next one, y must be 7 to get 12/4 = 3. </p>

<p>We have our x, w, and y; those are all we need. w = 3, x = 5, y = 7.</p>

<p>wy = 21
(x^2) - 4 = (5^2) - 4 = 21
Answer is E.</p>

<p>2) So I don’t know any cool tricks to answer this, but, when I was answering it, I found a pattern:</p>

<p>Starting from 3, if you divide 90/3 you get 30. If you minus it by 1, to get 29, you can add 29, 30, and 31 to get 90. So, it works for 3. Now the pattern starts here: If you divide 90 by 4, you get 22.5, and if you subtract by 1.5 (up .5 from the 1 from before), you get 21, and if you add 21, 22, 23, 24, you get 90. </p>

<p>If you do the same thing for 5, 90/5 = 18, and increase 1.5 to 2 and then subtract by it, you get 16. Add 16, 17, 18, 19, 20, and you get 90. Everything breaks down for 6, and that’s why 6 is the answer. If you think that doesn’t make any sense, go check it for 9: increasing by .5 up to 9, you get 4. 90/9 = 10, minus that by 4 and you get 6. 6+7+9+10+11+12+13+14 = 90, so…yea</p>

<p>3) Well, for this, you’ve got to do circumference measurements. Don’t think about just 1 clock, but rather make 2 circles, 1 which has point A on it, and one with point B. Basically, the circle with point B (the hour hand one) will have half a radius.</p>

<p>2pr = C. If you want, put some random number for R for point A, and divide it by 2 for Point B, but that isn’t exactly necessary. Instead, for point B, just divide 2pr/2, to get just pr. The actual key thing here is to think about the distance they’d travel. To make it easy for ourselves, let’s just say in 3 hours the minute hand will travel 1/4 of the clock, and, in 9 hours, the hour hand will travel 3/4. If you basically do 1/4 * 2pr (for the minute hand), you get .5pr. If you do 3/4 * pr, you get .75pr. If you do the ratios, you can bring .75 up to 3, and .5 up to 2, making it 2:3.</p>

<p>Ok, it may seem like a lot of words, but, when actually doing the calculations and thinking of it, it’ll go MUCH faster. Also, I’d like someone else to check my work.</p>

<p>4) Since all of their legs are exactly the same lengths (they’re all diagonals of the faces), all of them must be the same angles, aka 60.</p>

<p>5) First, figure out how many minutes are in 7.5 hours. It’s 450 minutes. Now figure out what 1 painter can do in 450 minutes. Well, 90 minutes (which is how much it takes 1 painter to do 2 rooms) goes into 450 five times, so he can do 10 rooms (2 rooms*5) in 450 minutes. In that case, using the same reasoning, we just need 4 more painters to do 50 rooms (4 more painters can do a total of 40 rooms, and add that with the original, and we get 50).</p>

<p>6) Ok, so I might be wrong here, but I’ll say what I thought of so far:</p>

<p>If g(k) = g(2k-3), you can think of g(2k-3) as g(x), and so g(2k-3) = 2(2k-3)-3, which is also 4k-9.
So, that means g(k) = 4k-9. g(4k) = 4(4k)-9 = 16k-9.
Still, I’m not so sure about it, so please someone check for me.</p>

<p>7) Yes, I think you’re right. 4x3x2x1 = 24</p>

<p>8) You’ve got the right idea, considering the marks you’ve put.</p>

<p>If the 60 side = 9, then 9 = x * sqrt(3), square everything to get 81=3(x^2). Divide by 3 to get 27=x^2, or sqrt(27) = x. Since the 90 side = 2x = 2<em>sqrt(27), do 2x + 2x = 4x AKA 4</em>sqrt(27). If you use a calculator, you can see that 12<em>sqrt(3) is equal to 4</em>sqrt(27). Sorry if this a little messy, but this technique works perfectly fine for me, although I’m sure there’s better.</p>

<p>wow, thank you SO much emidank! I wish there were more people like you here, so helpful and kind! thank you for taking the time to type up that monster of words/ explanations! i really appreciate it :)</p>

<p>6)</p>

<p>g(k)=g(2k-3)
2k-3=2(2k-3)-3
2k-3=4k-6-3
2k-3=4k-9
6=2k
3=k</p>

<p>g(4k)=g(4(3))=g(12)=2(12)-3= 24-3= 21</p>

<p>why did you substitute 2k-3 for g(k) in your second step? isn’t it g(k)= g(2k-3),
NOT g(k)= 2k-3? </p>

<p>thanks so much if you could explain!!</p>

<br>

<br>

<p>I want to point out the error here. The minute hand will actually travel around the clock three times.</p>

<p>Let minute hand length = 6;
Let hour hand length = 3;
Note that circumference formula = 2(pi)r;
Hand A travels around the clock 3 times;
Hand B travels around the clock 3/4 times;</p>

<p>Hand A total distance: (3)(2)(pi)(6) = 36pi
Hand B total distance: (3/4)(2)(pi)(3) = 4.5pi</p>

<p>Ratio is 36:4.5 –> 72:9;
Simplifies to 8:1;</p>

<p>@teteatete</p>

<p>Yea, I knew I had something wrong…I had tried your technique as well, but I made a slight mistake and got a ratio of 36:9 instead of your 36:4.5, so I considered it wrong and did something else. thanks for that though</p>

<p>btw can someone properly explain that g(k) question? </p>

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<p>I really don’t get how to do this!</p>

<p>The function is g(x) = 2x - 3;
g(k) = g(2k - 3);
Therefore 2k - 3 = 2(2k-3) - 3;
Now let’s do some algebra.
2k - 3 = 4k - 6 - 3;
2k - 3 = 4k - 9;
2k = 6;
k = 3;
Now it’s time to plug k = 3 back into the expression: g(4k) = …
4k = 4(3) = 12;
g(12) = (2)(12) - 3;
g(12) = 24 - 3;
The final answer, therefore, is 21.</p>

<p>Hopefully you can follow that. I tried to make the steps exceptionally simple.</p>

<p>@teteatete can you explain the transition from the 2nd line to the 3rd line?</p>

<p>Actually I realize that plugging in the expression to the function is unnecessary.
All I’m doing is solving for k because k = 2k - 3;
It’s clear that k = 3, right?
Now just plug k back into g(4k) where 4k = 12.
Solve for g(12) based on the given function.</p>

<p>Sorry, Houston, I missed your comment.
In my original post I plugged in the values k and 2k - 3 into the [x] of the original function g(x) = 2[x] - 3 but later realized that it’s completely redundant.</p>

<p>Thank you! One more question; in the the clock problem, the fact that the minute hand is twice as long as the hour hand is irrelevant right?</p>

<p>oh wait just kidding haha</p>

<p>could you explain the 2nd problem?
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<p>Sure thing! I love doing these problems.
Basically, you’re trying to find if 90 can be divided into z number consecutive integers. The best way to solve this problem is probably just to test out every answer.</p>

<p>A. 3: 29 + 30 + 31 = 90
B. 4: 21 + 22 + 23 + 24 = 90
C. 5: 16 + 17 + 18 + 19 + 20 = 90
D. There is no way to make 90 out of six consecutive integers.
E. 9: 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 = 90</p>

<p>One thing that’s cool to note is that all ODD values of z, when you divide 90 by it/them (ok forget grammar for right now), should yield the median of the set. All even values CANNOT yield a whole integer for them to work because both sides of the median have to be equivalent.</p>

<p>To solve this algebraically, you would simply see that:
90/6 = 15. Because you need 6 terms and cannot skip 15, you can’t possibly form a series which adds up to 90. e.g. 13 + 14 + 15 + 16 + 17 + 18 = 93 (does not work)</p>

<p>Check out the other even z:
90/4 = 22.5. 22.5 is equidistant and therefore compensated for by the consecutive numbers 22 + 23. This is in line with out general rule of thumb.</p>

<p>Basically, the answer is D. Again, I apologize if any of my explanation is unclear and would be happy to explain any parts more in depth.</p>

<p>ah thank you so much for your help!</p>

<p>Also, if you didn’t want to work out the math in your head, a sum of consecutive integers can be expressed as x + x + 1 + x + 2 + … + x + n-1 (where n is the number of consecutive integers). Knowing the above, you can set</p>

<p>A) 3x + 3 = 90
B) 4x + 6 = 90
C) 5x + 10 = 90
D) 6x + 15 = 90
E) 9x + 36 = 90</p>

<p>Whichever one of these does not result in an integer answer for x is the answer. D.</p>

<p>@teteatete</p>

<p>you said:
“The function is g(x) = 2x - 3;
g(k) = g(2k - 3);
Therefore 2k - 3 = 2(2k-3) - 3;”</p>

<p>^i’m sorry, but I still don’t understand how you plugged in 2k-3 for g(k)?
doesn’t g(k)= g(2k-3), not just 2k-3?</p>

<p>thanks so much!</p>