Average: A single number that gives a measure of central tendency of the numbers in a set. Usually, this is the mean. (It could also be the median or the mode.)

Base of a percent: The number for which the percent is found. For example, in the problem 10% of 50, the base is 50.

Base ten: A number system in which each digit has 10 times the value of the same digit one place to its right. For example, with 77 , the 7 to the left is worth 70, or 10 times the value of the 7 to the right.

Decimal (decimal number): A number written using base ten; a number containing a decimal point.

Decimal point: A dot separating the ones and the tenths places in a decimal number.

Denominator: The quantity below the line in a fraction. It tells the number of equal parts into which a whole is divided.

Difference: The amount that remains after one quantity is subtracted from another.

Digit: Any one of following ten symbols: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}.

Equivalent: Two expressions that name the same number. For example, 4.6 and 4.60 are equivalent decimals; 2/3 and 4/6 are equivalent fractions; and 2:6 and 1:3 are equivalent ratios.

Estimate: A number that is an approximatio n to an exact amount.

Fraction: A way of representing part of a whole or part of a group by telling the number of equal parts in the whole and the number of those parts that are being described. For example, in the fraction 4/5 , there are 5 parts in the whole and 4 of those parts are being described.