We cannot take half of 9 people. The even numbers, then, are the numbers divisible by 2: 2, 4, 6, 8, and so on. The odd numbers are 1, 3, 5, 7, and so on. If you do not know half of some even number, you can find it by decomposing it mentally into two even numbers whose half you do know.
To draw a shape, line or angle accurately using a compass and straightedge (ruler). Sometimes you are also allowed to use a protractor and triangle.
Geometry is one of the classical disciplines of math. Roughly translating in Greek as Earth Measurement, it is concerned with the properties of space and figures. It is primarily developed to be a practical guide for measuring lengths, areas, and volumes, and is still in use up to now.