Percent problems and financial mathematics

2010006208

Level: 
B
There are \(14\) right-handed and \(18\) left-handed children among the children attending the ceramic group. Find the difference between percentages of right-handers and left-handers in the group. (Round the result to one decimal place.)
differ by \(27.3\, \%\)
differ by \(63.6\, \%\)
differ by \(36.4\, \%\)
differ by \(57.1\, \%\)

2010006209

Level: 
B
The angle \( \beta \) is by \( 20\% \) smaller than the angle \( \gamma \) and by \( 100\% \) greater than the angle \( \alpha \). The angle \( \alpha \) is
by \( 60\% \) smaller than \( \gamma \).
by \( 40\% \) smaller than \( \gamma \).
by \( 20\% \) smaller than \( \gamma \).
by \( 80\% \) smaller than \( \gamma \).

2010018203

Level: 
B
A protective layer of thickness \(d\) reduces the level of harmful radiation by \(10\%\). Determine what is the percentage decrease in the original level of harmful radiation after passing through the layer of thickness \(3d\). Round the result to the whole percent.
\(73\%\)
\(70\%\)
\(30\%\)
\(27\%\)

2010018204

Level: 
B
The aluminium rod and brass rod have the same length at a given temperature. The material constants of the rods are: \(\alpha_{\mathrm{aluminium}}=24\cdot 10^{-6}\,\mathrm{K}^{-1}\) and \(\alpha_{\mathrm{brass}}=18\cdot 10^{-6}\,\mathrm{K}^{-1}\). Suppose both rods are heated to the same higher temperature. Find the true statement about the extensions of both rods. Round the percentage difference in the rods’ extensions to the whole percent. \[~\] Hint: Solid materials expand upon heating. The rod with the initial length \(l_0\) is upon the temperature increasing by \(\Delta t\) extended by the value \(\Delta l = l_0 \cdot \alpha \cdot \Delta t\), where \(\alpha\) is the material constant (coefficient of linear thermal expansion) that is indicative of the extent to which a material expands upon heating.
The extension of the aluminium rod is by \(33\%\) greater than the extension of the brass rod.
The extension of the aluminium rod is by \(67\%\) greater than the extension of the brass rod.
The extension of the aluminium rod is by \(133\%\) greater than the extension of the brass rod.
The extension of the aluminium rod is by \(33\%\) less than the extension of the brass rod.