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

Hundred : Hundred refers to the number 100.

Meter : A meter is a unit for measuring length.

Mile : A mile is a unit for measuring length. One mile is about 1609 meters.

Rounding : Rounding is the operation of changing a number to a number that is close to the original number. Rounded numbers are often used to do quick rough calculations for estimation purposes. For example rounding $4549$ to the nearest thousand results in 5000, rounding the same number to the nearest hundred results in 4500. In general one rounds up if the digit after the digit we try to round to is 5 or more, otherwise one rounds down.

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.

Equivalent equation : Equivalent equations are equations that have the same set of solutions. Adding the same number to both sides of an equation results in an equivalent equation and so does multiplying both sides of an equation by a number that is not equal to zero.

Infinity : Infinity or $\infty$ represents a number that is bigger than all numbers in $\mathbb{R}.$

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.