Count : To count means to find out the number of objects by adding one for every object.

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

Denominator : The denominator of a fraction $\frac{a}{b}$ is the number $b$ below the fraction bar.

Fraction : A fraction is a number that can be written as $\frac{a}{b}$ with an integer $a$ and a natural numbers $b.$ A fraction $\frac{a}{b}$ is the result of the division $a\div b.$ Examples of fractions are $\frac{1}{2}, -\frac{2}{3}$ and $\frac{3}{2}.$

Greatest common factor : The greatest common factor of two natural numbers $m$ and $n$ is a natural number $k$ that is a factor of $m$ and $n$ such that there is no bigger number that is also a factor of $m$ and $n.$ For example the greatest common factor of 12 and 15 is 3. To simplify a fraction one can divide both the numerator as well as the denominator by the greatest common factor of the numerator and the denominator. The exponents in the prime factorization of the greatest common factor of two numbers are the minima of the exponents in the prime factorization of the two numbers.

Half : A Half is the number equal to $\frac{1}{2}=0.5.$

Numerator : The numerator of a fraction $\frac{a}{b}$ is the number $a$ above the fraction bar.

Reduced fraction : A reduced fraction (or simplified fraction or fraction in simplified form or fraction in simplest form) is a fraction $\frac{a}{b}$ such that $a$ and $b$ do not have any common factors bigger than 1. For example the reduced fraction of the fraction $\frac{4}{6}$ is $\frac{2}{3}.$

Impossible : An event is impossible if it has a probability of 0.

Outcome : A result of a random experiment.

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.

Unlikely : An event in a probability experiment in unlikely if the probability of it happening is low.