1991 年

$3\text{ kg}$ of a solution contains $40\%$ of alcohol by weight. How much alcohol should be added to obtain a solution containing $50\%$ of alcohol by weight?

$P$ sold an article to $Q$ at a profit of $25\%$. $Q$ sold it to $R$ also at a profit of $25\%$. If $Q$ gained $\$500$, how much did $P$ gain?

From a rectangular metal sheet of width $3\text{ cm}$ and length $40\text{ cm}$, at most how many circles each of radius $1\text{ cm}$ can be cut?

Questions 45 and 46 refer to the figure below, which shows a cuboid $ABCDEFGH$ with $AE=2a$, $EF=2b$ and $FG=2c$. $AC$ and $BD$ intersect at $X$.

$XE=$

Questions 45 and 46 refer to the figure below, which shows a cuboid $ABCDEFGH$ with $AE=2a$, $EF=2b$ and $FG=2c$. $AC$ and $BD$ intersect at $X$.

If the angle between $XE$ and the plane $EFGH$ is $\theta$, then $\tan\theta=$

$\cos\dfrac{\pi}{2}+\cos\pi+\cos\dfrac{3\pi}{2}+\cos 2\pi+\cdots+\cos 10\pi=$

The figure shows the graph of the function

In the figure, the height of the vertical pole $PO$ is

In the figure, find the length of $AB$, correct to the nearest cm.

In the figure, $ABC$ and $CDE$ are equilateral triangles. Find $\angle ADE$.