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

Matrix : A $m\times n$ matrix is a rectangular arrangement of $m\cdot n$ numbers into $m$ rows and $n$ columns. For example $\begin{pmatrix}1&2&3\\4&5&6\\\end{pmatrix}$ is a $3\times 2$ matrix. $A_{ij}$ refers to the element of $A$ in the i-th row and j-th column.

Skip count : Skip counting refers to repeatedly adding the same number to a starting number. For example skip counting in twos starting at 3 results in 3, 5, 7, 9... Skip counting in threes starting in 1 results in 1, 4, 7, 10,...

Addition : Addition is the mathematical operation that describes increasing a number by an amount equal to a second number. The mathematical symbol for addition is the plus sign $+.$ The term addition is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

Division : Division is the mathematical operation that divides objects equally into groups. More generally $x\div y$ is defined as the number that if multiplied by $y$ equals $x.$

Product : A product is the result of a multiplication.

Subtraction : Subtraction is the mathematical operation that describes decreasing a number by an amount equal to a second number. The mathematical symbol for subtraction is the minus sign $-.$ The term subtraction is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

Division : Division is the mathematical operation that divides objects equally into groups. More generally $x\div y$ is defined as the number that if multiplied by $y$ equals $x.$

Equation : An equation is a mathematical statement in which two expressions are written with an equal sign in between. A solution of an equation is a set of variables that makes the statement a true statement.

Solution : A solution to an equation is a choice of variables that when substituted into the equation results in a true statement.

Subtraction : Subtraction is the mathematical operation that describes decreasing a number by an amount equal to a second number. The mathematical symbol for subtraction is the minus sign $-.$ The term subtraction is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.