A

9000139707

Level: 
A
A Morse code utilized dots and dashes to encode letters of an alphabet. Find the number of signals of the length from \(1\) to \(4\) which can be obtained from dots and dashes.
\(2 + 2^{2} + 2^{3} + 2^{4}=30\)
\(1 + 2 + 3! + 4!=33\)
\(\frac{4!} {3!\, 2!}=2\)
\(2 \cdot 1 + 2 \cdot 2 + 2 \cdot 3 + 2 \cdot 4=20\)

9000140002

Level: 
A
Solve the following equation with unknown \(x\) and a real parameter \(a\in\mathbb{R}\setminus\{0\}\). \[ \frac{x+a} {a} = ax - 1\]
\(\begin{array}{cc} \hline \text{Parameter} & \text{Solution set}\\ \hline a\in\{-1,1\} & \emptyset \\ a\notin\{-1,0,1\} & \left\{\frac{2a}{(a-1)(a+1)}\right\} \\\hline \end{array}\)
\(\begin{array}{cc} \hline \text{Parameter} & \text{Solution set}\\ \hline a=-1 & \emptyset \\ a\notin\{-1,0\} & \left\{\frac{2a}{(a-1)(a+1)}\right\} \\\hline \end{array}\)
\(\begin{array}{cc} \hline \text{Parameter} & \text{Solution set}\\ \hline a\in\{-1,1\} & \mathbb{R} \\ a\notin\{-1,0,1\} & \left\{\frac{2a}{(a-1)(a+1)}\right\} \\\hline \end{array}\)

9000121708

Level: 
A
Consider a square \(ABCD\) and a point \(E\) on the side \(BC\) such that the angle \( BAE\) has measure \(20^{\circ }\). The point \(F\) is on the side \(CD\) and the length of \(AF\) equals to the length of \(AE\) (i.e. the triangle \(AEF\) is isosceles with \(AF\) and \(AE\) of equal length). Find the measure of the angle \( AEF\).
\(65^{\circ }\)
\(45^{\circ }\)
\(50^{\circ }\)
\(70^{\circ }\)

9000121709

Level: 
A
Consider a rectangle \(ABCD\) of a special ratio between the length and the width: if \(E\), \(F\), \(G\) and \(H\) denote the midpoints of the sides \(AB\), \(BC\), \(CD\) and \(DA\), respectively, then the measure of the angle \( AEH\) is \(25^{\circ }\). Find the measure of the angle \( EFG\).
\(50^{\circ }\)
\(65^{\circ }\)
\(75^{\circ }\)
\(130^{\circ }\)

9000121807

Level: 
A
In the figure the cut of a regular polygon with unspecified number of vertices is shown. The red angle is the central angle of the polygon, the blue angle is the interior angle of the polygon. Suppose we consider a regular polygon with the central angle of \(40^{\circ}\), then find the measure of the interior angle of this polygon.
\(140^{\circ }\)
\(80^{\circ }\)
\(200^{\circ }\)
\(120^{\circ }\)

9000120307

Level: 
A
The lengths of a side, base diagonal and solid diagonal through the vertex \(A\) in a rectangular box \(ABCDEFGH\) are \(|AB| = 6\, \mathrm{cm}\), \(|AC| = 10\, \mathrm{cm}\), \(|AG| = 15\, \mathrm{cm}\). Find the volume of the box.
\(240\sqrt{5}\, \mathrm{cm}^{3}\)
\(900\, \mathrm{cm}^{3}\)
\(300\sqrt{5}\, \mathrm{cm}^{3}\)
\(600\sqrt{2}\, \mathrm{cm}^{3}\)
\(240\sqrt{2}\, \mathrm{cm}^{3}\)