In the diagram below of right triangle ACB, altitude CD is drawn to hypotenuse AB. If AB = 45 and AC = 15, what is the length of AD?
1) 3
2) 5
3) 7
4) 9

White shapes and black shapes are used in a game. some of the shapes are circles. while the rest are squares. the ratio of the number of white shapes to the number of black shapes is 5: 11. the ratio of the number of white cicrles to the number of white squares is 3: 7. the ratio of the number of black circles to the number of black squres is 3: 8. work out what fraction of all the shapes are circles.