1997 College Scholastic Ability Test

Mathematics·Studies (I)

Hum. & Arts

What is the value of \((125^2-75^2)\div\{5+(30-50)\div(-4)\}\)? [2 points]

\(75\)
\(125\)
\(900\)
\(1000\)
\(1225\)

For \(\alpha=-2+i\) and \(\beta=1-2i\), what is the value of \(\alpha\overline{\alpha}+\overline{\alpha}\beta+\alpha\overline{\beta}+\beta\overline{\beta}\)? (※ \(\overline{\alpha}\) and \(\overline{\beta}\) are complex conjugates of \(\alpha\) and \(\beta\) respectively, and \(i=\sqrt{-1}\).) [2 points]

\(1\)
\(2\)
\(4\)
\(10\)
\(20\)

Let \(\alpha\) and \(\beta\,(\alpha>\beta)\) be the two solutions to the quadratic equation \(x^2-2\sqrt{3}x+2=0\). What is the value of \(\theta\) that satisfies \(\tan\theta=\dfrac{\alpha-\beta}{\alpha+\beta}\)?
(※ \(-\dfrac{\pi}{2}<\theta<\dfrac{\pi}{2}\)) [2 points]

\(\dfrac{\pi}{6}\)
\(\dfrac{\pi}{4}\)
\(\dfrac{\pi}{3}\)
\(-\dfrac{\pi}{4}\)
\(-\dfrac{\pi}{3}\)

For the matrix \(A=\begin{pmatrix}1&1\\2&3\end{pmatrix}\), a matrix \(B\) satisfies \(ABA=A\). Which option below is equal to \(A+B\)? [3 points]

\(\begin{pmatrix}2&2\\4&6\end{pmatrix}\)
\(\begin{pmatrix}2&0\\0&6\end{pmatrix}\)
\(\begin{pmatrix}-2&2\\4&2\end{pmatrix}\)
\(\begin{pmatrix}0&2\\4&0\end{pmatrix}\)
\(\begin{pmatrix}4&0\\0&4\end{pmatrix}\)

Mathematics·Studies (I)

Hum. & Arts

For the universe \(U\) and its two subsets \(A\) and \(B\), let us define

\(A*B=(A\cap B)\cup(A\cup B)^C\).

Which option below is not always true? (※ \(U\ne\varnothing\)) [2 points]

\(A*U=U\)
\(A*B=B*A\)
\(A*\varnothing=A^C\)
\(A*B=A^C*B^C\)
\(A*A^C=\varnothing\)

\(\log_2x\) and \(\log_2y\) have a relation depicted in the graph to the right. Which option below appropriately depicts the relation between \(x\) and \(y\)? [2 points]

Figure below is a circuit using \(10\) identical resistors (

). Which option below has the same topology with this circuit? [2 points]

The annual soft drink sales of some soft drink company greatly depends on the average temperature in summer that year. According to past data, the probability that the annual sales quota is reached is \(0.8\) if the average temperature in summer that year is higher than the previous year, \(0.6\) if it is about the same as the previous year, and \(0.3\) if it is lower than the previous year.
According to the weather forecast, the average temperature in summer next year will be higher than this year for a probability of \(0.4\), about the same as this year for a probability of \(0.5\), and lower than this year for a probability of \(0.1\). What is the probability that this company will reach quota in the next year? [2 points]

\(0.55\)
\(0.60\)
\(0.65\)
\(0.70\)
\(0.75\)

Mathematics·Studies (I)

Hum. & Arts

Consider a point \(\mathrm{A}(-1,0)\) on the parabola \(y=x(x+1)\). A point \(\mathrm{P}\) moves along the parabola, starting from point \(\mathrm{A}\), and approaches the origin \(\mathrm{O}\) arbitrarily closely. what is the limit of the size of \(\angle\mathrm{APO}\)? [3 points]

\(90°\)
\(120°\)
\(135°\)
\(150°\)
\(180°\)

A polynomial function \(P(x)\) satisfies the following identity.

\(P(P(x)+x)=(P(x)+x)^2-(P(x)+x)+1\)

What is the value of \(P'(0)\)? [3 points]

\(-2\)
\(-1\)
\(0\)
\(1\)
\(2\)

In one region, there are three high schools \(\mathrm{A, B}\) and \(\mathrm{C}\) each with \(500\) third-grade students, whose math scores each follow a normal distribution as the figure shows. Which option contains every correct statement in the <List>? [3 points]

There are more students with excellent scores in school \(\mathrm{A}\) than school \(\mathrm{B}\).
On average, students of school \(\mathrm{B}\) have better scores than students of school \(\mathrm{A}\).
The scores of students of school \(\mathrm{B}\) are less spread out than students of school \(\mathrm{C}\).

a
b
c
a, c
b, c

In some year, the monthly salary of newly recruited college graduates in Korea, USA, and Japan follow normal distributions with a mean of \(800,000\) won, \(2,000\) dollars, and \(180,000\) yen respectively, and a standard deviation of \(100,000\) won, \(300\) dollars, and \(25,000\) yen respectively. Three newly recruited college graduates \(\mathrm{A, B}\) and \(\mathrm{C}\) were randomly chosen from each of the three nations above, and their monthly salaries were \(940,000\) won, \(2,250\) dollars, and \(210,000\) yen respectively. Which option below orders the three people from the one who relatively earns the most compared to their nation, to the one who relatively earns the least? [2 points]

\(\mathrm{A,B,C}\)
\(\mathrm{A,C,B}\)
\(\mathrm{B,A,C}\)
\(\mathrm{C,A,B}\)
\(\mathrm{C,B,A}\)

Mathematics·Studies (I)

Hum. & Arts

As the figure shows, \(\mathrm{A}\) and \(\mathrm{B}\) move in the same direction along a line. \(\mathrm{B}\) starts moving at the same time with \(\mathrm{A}\), \(200\) meters ahead of \(\mathrm{A}\).
Let \(a_1\) be the starting position of \(\mathrm{A}\), \(a_2\) be the starting position of \(\mathrm{B}\), \(a_3\) be the position of \(\mathrm{B}\) when \(\mathrm{A}\) reaches \(a_2\), and \(a_4\) be the position of \(\mathrm{B}\) when \(\mathrm{A}\) reaches \(a_3\). Continue this process for all points \(a_n(n=1,2,3,\cdots)\). If the velocity of \(\mathrm{A}\) is \(2\) times the velocity of \(\mathrm{B}\), what is the position of \(\mathrm{A}\) when the distance between \(\mathrm{A}\) and \(\mathrm{B}\) becomes less than \(1\) meter? [3 points]

Between \(a_4\) and \(a_5\)
Between \(a_6\) and \(a_7\)
Between \(a_8\) and \(a_9\)
Between \(a_{10}\) and \(a_{11}\)
Between \(a_{12}\) and \(a_{13}\)

A function \(f(x)\) defined for all real numbers is a periodic function satisfying \(f(x)=x^2\,(-1\leq x\leq1)\:\) and \(\:f(x+2)=f(x)\). On the \(xy\)-plane, for all positive integers \(n\), let \(a_n\) be the number of intersections between the line \(y=\dfrac{1}{2n}x+\dfrac{1}{4n}\) and the graph of the function \(y=f(x)\). What is the value of \(\displaystyle\lim_{n\to\infty}\!\frac{a_n}{n}\)? [2 points]

\(0\)
\(1\)
\(2\)
\(3\)
\(4\)

The two tangent lines to the parabola \(y=(x-a)^2+b\) at points \(\mathrm{P}(s+a,s^2+b)\) and \(\mathrm{Q}(t+a,t^2+b)\) respectively, are perpendicular to each other. Let \(A\) be the area of the shape enclosed by these two tangent lines and the parabola. Which option contains every correct statement in the <List>? [2 points]

If \(s\) increases, \(t\) also increases.
If \(a\) increases, the area \(A\) also increases.
If \(b\) changes, the area \(A\) also changes.

a
b
c
a, c
b, c

Members of the ‘base-\(12\) society’ write integers by using the mapping shown in the table below.

Base-\(10\)	\(1\;\:2\;\:3\;\:4\;\:5\;\:6\;\:7\;\:8\;\:9\;\:10\;\:11\;\:12\;\:13\;\:\cdots\)
Base-\(12\)	\(1\;\:2\;\:3\;\:4\;\:5\;\:6\;\:7\;\:8\;\:9\;\;\:x\;\;\:y\;\:\:\,10\;\:11\;\:\cdots\)

Some examples of addition in base-\(12\) are

\(1+9=x\:\) and \(\:x+y=19\).

For two base-\(12\) numbers \(xxx\) and \(yyy\), what is their sum \(xxx+yyy\) written in base-\(12\)? [3 points]

\(1779\)
\(2331\)
\(1xx9\)
\(1yy9\)
\(1yyx\)

Mathematics·Studies (I)

Hum. & Arts

The flowchart to the right is an algorithm finding the smallest positive integer \(n\) for which the inequality \(2^{n+1}<9n^4\) is false. What are appropriate for \((\alpha), (\beta)\) and \((\gamma)\) in the flowchart to the right in this order? [2 points]

\(S\!\gets\!S\!+\!2,\;S\geq 9N^4,\:\) Print \(N+1\)
\(S\!\gets\!S\!\times\!2,\;S< 9N^4,\:\) Print \(N\)
\(S\!\gets\!S\!\times\!2,\;S< 9N^4,\:\) Print \(N+1\)
\(S\!\gets\!S\!\times\!2,\;S\geq 9N^4,\:\) Print \(N\)
\(S\!\gets\!S\!\times\!2,\;S\geq 9N^4,\:\) Print \(N+1\)

The following is the middle part of a proof of the statement 「If \(x^2+y^2+z^2=1111\), then \(\fbox{\(\;(\alpha)\;\)}\)」.

<Proof>
\(\cdots\) (omitted) \(\cdots\)
In the division of integers \(x, y\) and \(z\) by \(8\),
the remainder is among \(0,1,2,3,4,5,6\) or \(7\). Therefore, in the division of \(x^2, y^2\) and \(z^2\) by \(8\), the remainder is among \(0,1\) or \(4\). Therefore, in the division of \(x^2+y^2+z^2\) by \(8\), the remainder is among \(0,1,2,3,4,5\) or \(6\). However, the division of \(1111\) by \(8\) has remainder \(7\).
\(\cdots\) (omitted) \(\cdots\)

What is appropriate for \(\fbox{\(\;(\alpha)\;\)}\) above? [2 points]

at least one among \(x, y\) and \(z\) is an integer.
none among \(x, y\) and \(z\) are integers.
there is at least one solution where \(x, y\) and \(z\) are all integers.
there is only one solution where \(x, y\) and \(z\) are all integers.
there are no solutions where \(x, y\) and \(z\) are all integers.

As the figure shows, a quadrilateral \(\mathrm{ABCD}\) is inscribed in a circle, and its two diagonals \(\mathrm{AC}\) and \(\mathrm{BD}\) meet at point \(\mathrm{P}\) perpendicular to each other. Let \(\mathrm{E}\) be the perpendicular foot from point \(\mathrm{P}\) to edge \(\mathrm{BC}\), and let \(\mathrm{F}\) be the point where line \(\mathrm{PE}\) meets the edge \(\mathrm{AD}\). Which option below cannot be proven from this? [3 points]

\(\angle\mathrm{CBP}=\angle\mathrm{PAD}\)
\(\angle\mathrm{APF}=\angle\mathrm{PAF}\)
\(\angle\mathrm{FPD}=\angle\mathrm{FDP}\)
\(\overline{\mathrm{AF}}=\overline{\mathrm{FD}}\)
\(\overline{\mathrm{AP}}=\overline{\mathrm{AF}}\)

Consider triangles with internal angles of \(30°,60°\) and \(90°\) that are congruent to each other. As the figure shows, let us put these triangles together without overlap such that the vertex with angle \(90°\) of one triangle matches the vertex with angle \(60°\) of the previous triangle, and the triangle is attached to the hypotenuse of the previous triangle. Let us put as many triangles together as possible while no triangles overlap each other. What is the greatest number of triangles that can be put together? [3 points]

\(6\)
\(8\)
\(10\)
\(12\)
\(14\)

† Assume no triangles are reflections of each other.

Mathematics·Studies (I)

Hum. & Arts

It is the summer of the year \(2525\), and you are making plans for January \(2526\). You have the calendar of the current year (\(2525\)) from January to December, but you don't have the calendar for the New Year (January \(2526\)). What month in the \(2525\) calendar has the same number of dates, on the same day of the week, as the January \(2526\) calendar? [3 points]

March
May
July
August
No such month.

The electrons of some atom can be in three states \(a,b\) or \(c\) according to the variations in energy. Suppose the following rules hold.

Rule \(1\): If the energy increases, electrons in state \(b\) rise to state \(c\), and electrons in state \(a\) either rise to state \(b\) or to state \(c\).

Rule \(2\): If the energy decreases, electrons in state \(b\) fall to state \(a\), and electrons in state \(c\) either fall to state \(b\) or to state \(a\).

In <Phase \(1\)>, an electron is in state \(a\). If the energy increases to <Phase \(2\)>, this electron will be in state \(b\) or state \(c\). There are \(2\) possible paths for this electron, namely \(a\to b\) and \(a\to c\). If the energy decreases again to <Phase \(3\)>, the possible paths for this electron until this point is \(3\), namely \(a\to b\to a\), \(a\to c\to b\), and \(a\to c\to a\).
If the energy keeps alternately increasing and decreasing in this fashion, what is the number of possible paths for this electron from <Phase \(1\)> to <Phase \(7\)>? [3 points]

\(18\)
\(19\)
\(20\)
\(21\)
\(22\)

Pro- duct	Base material \((\text{kg})\)	Electrical energy \((\text{kw}\cdot\text{h})\)
\(\mathrm{A}\)	\(1\)	\(2\)
\(\mathrm{B}\)	\(2\)	\(1\)

In some factory, the amount of base material\((\text{kg})\) and electrical energy\((\text{kw}\cdot\text{h})\) needed to produce \(1\) unit of products \(\mathrm{A}\) and \(\mathrm{B}\) are shown in the table. The available base material is \(40\text{kg}\), and electrical energy cannot be used more than \(60\text{kw}\cdot\text{h}\). The profit per \(1\) unit of products \(\mathrm{A}\) and \(\mathrm{B}\) are \(40,000\) won and \(30,000\) won respectively. What is the maximum profit attainable in this factory by producing units of products \(\mathrm{A}\) and \(\mathrm{B}\)?
(※ Units can only be sold whole) [4 points]

\(1,220,000\) won
\(1,240,000\) won
\(1,260,000\) won
\(1,280,000\) won
\(1,360,000\) won

Suppose, in a rectangular theater, we want to distinguish seats with a good view of the stage. Figure below is the floor plan of the theater. The width of the center stage is \(6\) meters, with \(\mathrm{A}\) and \(\mathrm{B}\) being the left and right ends of the stage. For a point \(\mathrm{X}\) in the theater, let \(\angle\mathrm{AXB}=\theta\). We want to put special class seats in the region where the angle \(\theta\) is \(30°\) or more, and put first class seats in the region where the angle \(\theta\) is between \(15°\) and \(30°\). What is the area of the region where we want to put first class seats? (Unit: meters\(^2\)) [4 points]

\(3\pi(12+11\sqrt{3})+18\)
\(3\pi(24-11\sqrt{3})+18\)
\(10(24-11\sqrt{3})+18\)
\(9(14+11\sqrt{3})\)
\(9(26-11\sqrt{3})\)

Mathematics·Studies (I)

Hum. & Arts

Short Answers (25~30)

As the figure shows, a square tile is laid on the \(xy\)-plane with its horizontal and vertical sides aligning with the \(x\)-axis and \(y\)-axis, respectively. Suppose we color inside this tile with blue and yellow, with the graphs of \(y=f(x)\) and \(y=g(x)\) being the boundaries of the colors. Given that the areas of the region colored blue and the region colored yellow have a ratio of \(2:3\), compute \(\displaystyle\int_0^{15}f(x)dx\).
(※ \(g(x)\) is the inverse of the function \(f(x)\).) [2 points]

Let \(g(x)\) be the inverse of the function

\(f(x)=\begin{cases} \dfrac{71}{5}-\dfrac{19}{15}x & (x<12)\\\\ 1-2\log_3(x-9) & (x\geq12). \end{cases}\)

Compute the value of \(x\) that satisfies \((g\circ g\circ g\circ g\circ g)(x)=-3\).
(※ \((g\circ g)(x)=g\{g(x)\}\)) [3 points]

\(a\) and \(b\) are positive numbers, and \(\alpha+\beta+\gamma=\pi\). Given that \(a^2+b^2=3ab\cos\gamma\), Compute the maximum value of \(9\sin^2(\pi+\alpha+\beta)+9\cos\gamma\). [3 points]

Let \((a_1,a_2,a_3,a_4)\) be a permutation of the set \(A=\{1,2,3,4\}\). Let \(s_k\,(k=1,2,3)\) be the number of elements to the right of \(a_k\) in the permutation that are less than \(a_k\).
Let us denote the sum \(s_1+s_2+s_3\) as

\(|\,(a_1,a_2,a_3,a_4)\,|\).

For example,

\(\begin{align}|\,(2,4,3,1)\,|\: &=\:s_1+s_2+s_3\\ &=\:1+2+1\:=\:4.\end{align}\)

For all \(24\) permutations \((i_1,i_2,i_3,i_4)\) of the set \(A\), determine the value of \(|\,(i_1,i_2,i_3,i_4)\,|\) and compute the sum of all such values. [4 points]

Mathematics·Studies (I)

Hum. & Arts

Two polynomial equations \(P(x)=0\) and \(Q(x)=0\) have \(7\) and \(9\) distinct real solutions, respectively,
and the set

\(A=\{(x,y)\,|\,P(x)Q(y)=0\:\) and \(\:Q(x)P(y)=0,\)
\(\qquad\;\; x\) and \(y\) are real numbers\(\}\)

is an infinite set. Let \(B\) be a subset of \(A\) where

\(B=\{(x,y)\,|\,(x,y)\in A\:\) and \(\:x=y\}\),

and let \(n(B)\) be the number of elements in \(B\). Then, the value of \(n(B)\) varies according to \(P(x)\) and \(Q(x)\). Compute the maximum value of \(n(B)\). [4 points]

Using approximations \(\log_{10}2=0.301\) and \(\log_{10}11=1.041\), compute the value of \(\log_{10}275\), and round the result to the nearest hundredth. [2 points]