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.

Ones digit : The first digit left of the decimal point (or the digit furthest to the right if there is no decimal point). It counts multiples of 1.

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.

Tens digit : The tens digit is the second digit left of the decimal point. For example 31.2 and 32 both have tens digits equal to 3.

Estimation : Estimation is another word for finding a close but not necessarily exact solution to an arithmetic problem.

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

Ones digit : The first digit left of the decimal point (or the digit furthest to the right if there is no decimal point). It counts multiples of 1.

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.

Significant figure : Rounding a number to k significant figures means that one leaves the first $k-1$ digits unchanged and rounds the k-th digit up if the (k+1)-th digit is at least 5 and rounds it down otherwise. For example rounding the number 1234 to 2 significant digits results in 1200.

Box plot : A way to visualize data. The left end of the box plot coincides with the minimum of the data. Similar the right end of the box plot visualizes the maximum of the data. The left and right end of the box in the box plot correspond to the 25th and 75th quantile of the data and the line in the box represents the median of the data.

Minimum : The minimum of a set of numbers is the lowest of the numbers in the set. A function has a minimum at $x_0$ if $f(x_0)\leq f(x)$ for all $x.$