
associative property 
in addition and multiplication, the characteristic that allows you to add or multiply a group of numbers in any order and get the same answer. For example, in multiplication, (5 x 2) x 7 is equal to (7 x 2) x 5. 
CAT scan 
an image of an area of the body that is formed from a grouping of xrays on a computer. CAT scans are used to make a diagnosis in medical treatment. CAT stands for computerized axial tomography. 
distributive property 
in mathematics, a characteristic of numbers that allows you to multiply a group of numbers and get the same answer you would get if you multiplied each member of the group and then combined the answers. For example, 4 x (8 + 1 + 5) is equal to (4 x 8) + (4 x 1) + (4 x 5). 
power 
the number of times another number is multiplied by itself. Three to the fourth power is equal to 3 x 3 x 3 x 3, or 81. [1/7 definitions] 
Roman numeral 
a letter used as a number in the ancient Roman number system. The letter I equals 1, V equals 5, X equals 10, L equals 50, C equals 100, D equals 500, and M equals 1,000. In this system, a letter followed by one of equal or lesser value means the two are added; seven is VII, or 5+1+1. A letter followed by one of greater value means that the first is subtracted from the second; four hundred is CD, or 500100. 
ten 
the word for the Arabic numeral 10 and the Roman numeral X. [1/3 definitions] 
ticktacktoe 
a game for two players who take turns marking either an X or an O on a grid of nine squares. The winner is the first player who fills in three squares in a row with the same mark. 
xray 
to photograph, treat, or examine using xrays. [1/3 definitions] 
zap 
to strike or hit with laser beams, xrays, or microwaves. [1/2 definitions] 

