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Answers ( 1079 )
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    A B C D E

    Since AE = BE = AB, \(\Delta ABE\) is an equilateral triangle

    \(S_{ABE}=\dfrac{6^2\sqrt{3}}{4}=9\sqrt{3}\) (cm2)

    The area of the sector ABE is : \(\dfrac{6^2\pi.60}{360}=6\pi\) (cm2)

    The area of the shaded region is :

    \(\dfrac{6^2\pi.90}{360}.2-\left[9\sqrt{3}+2\left(6\pi-9\sqrt{3}\right)\right]=6\pi+9\sqrt{3}\) (cm2)

    The answer is : 6 + 9 + 3 = 18

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    We have :

    \(\dfrac{1}{3}\pi R^2h=\dfrac{1}{3}\pi.3R^2.\dfrac{1}{3}h=\dfrac{1}{3}\pi\left(\sqrt{3}R\right)^2.\dfrac{1}{3}h\)

    So, the radius must be increased by \(\sqrt{3}\) times or :

    \(\sqrt{3}.100-100\approx73\left(\%\right)\)

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    \(S_{WXYZ}=XY.YZ=XY.2VY=4.\dfrac{XY.VY}{2}=4S_{XYV}=4.\dfrac{4}{5}=\dfrac{16}{5}\) (unit2)

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    The answer is :

    \(\widehat{VEZ}=\widehat{AED}-\widehat{AEV}-\widehat{DEZ}=\dfrac{180^0.3}{5}-45^0-45^0=18^0\)

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    \(4x-12y=-19\Leftrightarrow12y=4x+19\Leftrightarrow y=\dfrac{1}{3}x+\dfrac{19}{12}\)

    The x-coordinates of the intersection points of the graphs satisfy :

    \(x^2-3x+3=\dfrac{1}{3}x+\dfrac{19}{12}\Leftrightarrow x^2-\dfrac{10}{3}x+\dfrac{17}{12}=0\)

    Since there are 2 intersection points, we can apply the Vieta's formulas. The answer is \(\dfrac{10}{3}\)

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    When the water level rises 1 in, the amount of water in the tank increases by : 10 x 15 x 1 = 150 (in3)

    The volume of each sphere is : \(\dfrac{4}{3}\pi\left(\dfrac{1}{6}:2\right)^3=\dfrac{1}{1296}\pi\) (in3)

    The answer is : \(150:\dfrac{1}{1296}\pi\approx61900\) (spheres)

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    The sum of the factors of 120 which are different from 3 and 8 is :

    4 + 5 + 6 + 10 + 12 + 15 + 20 + 24 + 30 + 40 + 60 + 120 = 346

    So, the answer is 346

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    We can easily prove that EFGH is a square

    \(\Rightarrow EH=EF=\dfrac{HF}{\sqrt{2}}=\dfrac{AB}{\sqrt{2}}=\sqrt{2}\left(m\right)\)

    The area of the sector EFH is : \(\dfrac{\left(\sqrt{2}\right)^2\pi}{4}=\dfrac{\pi}{2}\left(m^2\right)\)

    \(S_{EFH}=\dfrac{\left(\sqrt{2}\right)^2}{2}=1\left(m^2\right)\)

    The answer is : \(2\left(\dfrac{\pi}{2}-1\right)=\pi-2\approx1.14\)

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    The volume of the cup is : \(\left(\dfrac{6}{2}\right)^2\pi.12=108\pi\) (cm3)

    The volume of 48 tapioca bubbles is : \(108\pi-100\pi=8\pi\) (cm3)

    The volume of each tapioca bubble is : \(\dfrac{8\pi}{48}=\dfrac{\pi}{6}\) (cm3)

    The answer is : \(\sqrt[3]{\dfrac{\pi}{6}:\dfrac{4\pi}{3}}=0.5\) (cm)

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    The answer is : \(1029:\left(45+53\right)=10.5\) (hours)

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    \(BC^2=4AB.AC\Leftrightarrow AB^2+AC^2=4AB.AC\)

    \(\Leftrightarrow AB^2-4AB.AC+4AC^2=3AC^2\Leftrightarrow\left(AB-2AC\right)^2=3AC^2\)

    Since \(AB< AC,AB-2AC< 0\) and :

    \(AB-2AC=-\sqrt{3}AC\Leftrightarrow AB=\left(2-\sqrt{3}\right)AC\)

    \(\tan\widehat{C}=\dfrac{AB}{AC}=2-\sqrt{3}\Rightarrow\widehat{C}=15^0\Rightarrow\widehat{B}=75^0\)

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    Let v (mph), t(h), a(mi) be Bob's speed, the time Bob traveled and the answer

    \(\left\{{}\begin{matrix}\left(v+5\right)\left(t+1\right)=vt+50\\\left(v+10\right)\left(t+2\right)=vt+a\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}vt+v+5t+5=vt+50\\vt+2v+10t+20=vt+a\end{matrix}\right.\)

    \(\Rightarrow\left\{{}\begin{matrix}v+5t=45\\2v+10t=a-20\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}2v+10t=90\\2v+10t=a-20\end{matrix}\right.\)\(\Rightarrow a=110\)

    So, the answer is 110 miles

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    Let a,b be the lengths of the legs of the triangle (a > b > 0)

    The hypotenuse of the triangle is : 15 x 2 = 30 (units)

    \(\left\{{}\begin{matrix}ab=30.12\\a^2+b^2=30^2\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}a^2-2ab+b^2=180\\a^2+2ab+b^2=1620\end{matrix}\right.\)

    \(\Rightarrow\left\{{}\begin{matrix}\left(a-b\right)^2=\left(6\sqrt{5}\right)^2\\\left(a+b\right)^2=\left(18\sqrt{5}\right)^2\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}a-b=6\sqrt{5}\\a+b=18\sqrt{5}\end{matrix}\right.\)

    \(\Rightarrow2b=12\sqrt{5}\Rightarrow b=6\sqrt{5}\)

    So, the answer is \(6\sqrt{5}\) units

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    \(\left\{{}\begin{matrix}mn=\left(m+2\right)\left(n-2\right)\\mn=\left(m-2\right)\left(n+10\right)\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}mn-2m+2n-4=mn\\mn+10m-2n-20=mn\end{matrix}\right.\)

    \(\Rightarrow\left\{{}\begin{matrix}2m-2n+4=0\\10m-2n-20=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}8m-24=0\\n=m+2\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}m=3\\n=5\end{matrix}\right.\)

    The answer is : 3 x 5 = 15

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    Let v(mph) ,t(h) be John's velocity and the time the trip took, then vt is the distance between 2 houses

    \(\left\{{}\begin{matrix}\left(v-10\right)\left(t+2\right)=vt\\\left(v+20\right)\left(t-2\right)=vt\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}vt+2v-10t-20=vt\\vt-2v+20t-40=vt\end{matrix}\right.\)

    \(\Rightarrow\left\{{}\begin{matrix}2v-10t-20=0\\2v-20t+40=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}v=5t+10\\10t-60=0\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}v=40\\t=6\end{matrix}\right.\)

    The answer is : 40 x 6 = 240 (mi)

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    In 1 minute, they can do \(\dfrac{1}{30}\) of the job together and Gertrude can do \(\dfrac{1}{40}\) of the job alone, so Bertha can do : \(\dfrac{1}{30}-\dfrac{1}{40}=\dfrac{1}{120}\) of the job alone

    The answer is : 120 minutes = 2 hours

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    Let \(\overline{ab}\) be the number

    \(\overline{ba}=\overline{ab}+\overline{ba}-\overline{ab}=10a+b+10b+a-c\left(a+b\right)\)

    \(=11\left(a+b\right)-c\left(a+b\right)=\left(11-c\right)\left(a+b\right)\)

    So, the answer is 11 - c

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    Apply the Vieta's formulas, we have : \(\left\{{}\begin{matrix}r+s=-6\\rs=-2\end{matrix}\right.\)

    \(r^3+s^3=r^3+s^3+3rs\left(r+s\right)-3rs\left(r+s\right)\)

    \(=\left(r+s\right)^3-3rs\left(r+s\right)=\left(-6\right)^3-3.\left(-2\right).\left(-6\right)=-252\)

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    \(x=\dfrac{13-73y}{2}=\dfrac{13-73.3}{2}=-103\)

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    \(\sqrt{4}.\dfrac{2}{3}.\sqrt{9}.\sqrt{144}\sqrt{841}=2.\dfrac{2}{3}.3.12.29=1392\)

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Questions ( 94 )
  • Given the square ABCD. Draw M, N, P, Q on the sides AB, BC, CD, DA respectively. Let E, F, G be the midpoints of MQ, MP, NP respectively. What figure is quadrilateral MNPQ when A, E, F, G, B are collinear ?

  • Find the smallest positive integer n such that n(n + 1)(n + 2)\(⋮247\)

  • Given an isosceles trapezoid ABCD (BC // AD). Let M, N be the midpoints of BC, AD respectively. Draw point P on the opposite ray of AB. PN cuts BD at Q. Prove that MN is the bisector ray of \(\widehat{PMQ}\)

  • Given the rhombus ABCD with \(\widehat{B}=40^0\). Let E be the midpoint of BC. Draw \(AF\perp DE\). Find \(\widehat{DFC}\)

  • Calculate :

    \(\dfrac{1}{3+1}+\dfrac{2}{3^2+1}+\dfrac{4}{3^4+1}+\dfrac{8}{3^8+1}+...+\dfrac{2^{2006}}{3^{2^{2006}}+1}\)

  • a/ Factorise : x5 + x - 1

    b/ Write 10000000099 as a product of 2 integer which are greater than 1

     

     

     

  • a) Prove that :

    \(\left\{{}\begin{matrix}ax+by=m\\cx+dy=n\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=\dfrac{bn-dm}{bc-ad}\\y=\dfrac{cm-an}{bc-ad}\end{matrix}\right.\)

    b) Prove that :

    \(\left\{{}\begin{matrix}ax+by+cz=m\\dx+ey+fz=n\\gx+hy+iz=p\end{matrix}\right.\)

    \(\Rightarrow\left\{{}\begin{matrix}y=\dfrac{\left(fa-dc\right)\left(pa-gm\right)-\left(ia-gc\right)\left(na-dm\right)}{\left(fa-dc\right)\left(ha-gb\right)-\left(ea-db\right)\left(ia-gc\right)}\\z=\dfrac{\left(ha-gb\right)\left(na-dm\right)-\left(ea-db\right)\left(pa-gm\right)}{\left(fa-dc\right)\left(ha-gb\right)-\left(ea-db\right)\left(ia-gc\right)}\end{matrix}\right.\)

     

  • Prove that :

    \(ax^2+bx+c=a\left(x+\dfrac{b-\sqrt{b^2-4ac}}{2a}\right)\left(x+\dfrac{b+\sqrt{b^2-4ac}}{2a}\right)\)

    \(\left(a\ne0;b^2-4ac\ge0\right)\)

    Apply the formula above to factorise the following polynomials :

    \(6x^2-5x-6;3x^3+5x^2-12x;42-17x^2-15x^4\)

  • Given a regular hexagon ABCDEF. Let G, I be the midpoint of AF, a point on CF such that \(IC=\dfrac{1}{3}IF\). Which kind of triangle is \(\Delta IGE\) ? Why ?

  • Given \(\Delta ABC\). Let D, E, F be the midpoints of BC, CA and AB respectively. A line passing through A cuts DE, DF at M, N respectively. BN cuts CM at P. Find \(\widehat{FPE}\) 

  • I wrote the natural numbers from 1 to n. However, I forgot a number. So, the average of the numbers is \(\dfrac{599}{17}\). Find n and the number I forgot.

  • Find the sum of the roots of x3 + 9x - 5 and x3 - 15x2 + 84x - 165, given that each polynomial has only 1 root.

  • Find \(n\in Z^+\) : \(\dfrac{7n-12}{2^n}+\dfrac{2n-14}{3^n}+\dfrac{24n}{6^n}=1\)

  • Given \(\left|a-b\right|=\left|b-c\right|=\left|c-d\right|=\left|d-e\right|=\left|e-a\right|\)

    Prove that a = b = c = d = e

  • \(\Delta ABC\) has \(\widehat{A}=70^0\). The perpendicular bisector of BC cuts the bisector of the exterior angle at vertex A at T. Find \(\widehat{TBC}\)

  • Given 10 numbers such that each number equal the sum of the squares of 9 remaining numbers. Find 10 numbers

  • \(\Delta ABC\) isosceles at A has AB = AC = 8 cm ; the median BD = 6 cm. Find BC.

  • Given \(\left|x\right|-3=\left|y\right|+4=10-\left|z\right|\left(x,y,z\in R\right)\)

    Find the maximum value of y(x + z)

  • There are only three species in Magic Wood: 12 snakes, 23 mice and 31 cats. Whenever a snake eats a cat, it becomes a rat, but when the cat eats the mouse it becomes a snake. Moreover, when the snake eats the mouse, it becomes a cat. Find the maximum number of animals in Magic Woods when no one eats another.

  • In a box, there is 1 ball numbered 1 ; 2 balls are numbered 2, ..., 100
    balls numbered 100. I take the ball out of the box without looking. How many balls do I take at least to ensure that there are 10 balls numbered the same number ?

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