Angle : If two line segments (or rays) both start at a common point the opening between the two line segments is called an angle. The common point is called vertex of the angle. The size of an angle is measured in degrees.

Corner : A corner of a shape is a point in the shape such that this point does not lie on the line segment between any two other points in the shape. Every triangle has 3 corners and every quadrilateral has 4 corners.

Degree : For angles one degree is defined as the angle represented by a $\frac{1}{360}$ of the angle represented by a full circle. For measuring temperatures one can use either degrees Celsius or degrees Fahrenheit. In a polynomial the degree describes the highest exponent of $x$ that has a non-zero coefficient. For example the degree of $1+x+x^2$ is 2.

Line : A line AB is a one-dimensional shape that includes the points A and B, all the points on the line segment in between A and B and all the points of the straight extension of the line segment beyond A and B. A line does not have an endpoint.

Minus : Minus is either a symbol or another word for subtraction.

Perpendicular line : Two lines are called perpendicular if they cross in a right angle.

Right angle : A right angle is an angle equal to $90^{\circ}.$

Right triangle : A right triangle is a triangle that has a right angle. The sides that form the right angle are called legs, the third side is called hypotenuse. The area of a right triangle is half the product of the lengths of the two legs. The Pythagorean theorem is an important theorem for right triangles that allows to calculate the third side of a right triangle given the other two.

Sum : A sum is the result of an addition.

Triangle : A triangle is a polygon with three corners and three sides. You can calculate the area of a triangle by multiplying half the length of the base by the height on that base. The sum of the interior angles in a triangle is always $180^{\circ}.$

Decompose the triangle into two right triangles.

The correct answer is 180. Decompose the triangle into two right triangles by drawing a line through one of the corners that perpendicularly crosses the side below the corner. The sum of the angles of the original triangle is equal to the sum of the angles in the two right triangles minus the two right angles at the crossing. Because the sum of the angles in a right triangle is 180 degrees, the sum of angles in any triangle is $2\cdot 180-2\cdot 90=180$ degrees.

Decimal point : The point in a decimal separating the digits representing multiples of wholes from the digits representing fractions of wholes.

Calculate $8-4$ and put the decimal point in the right place.

The correct answer is 0.04. Because 8-4=4, we have 0.08-0.04=0.04.

Expected number : The expected number of $n$ repetitions of a random experiment that is described by a random variable $X$ is defined as $n\cdot E[X].$

Number : A number $x$ is a mathematical symbol representing a quantity.

Probability : A probability is a number between 0 and 1 that describes how likely an outcome is. For discrete events that are equally likely the probability can be calculated by dividing the number of favorable outcomes by the number of possible outcomes.

The expected number is the probability times the number of repetitions.

The correct answer is 700. The expected number is the probability times the number of repetitions, which is $\frac{1}{2}1400=700.$