10/21 * 7/15 = 2/3 * 1/3 = 2/9

9/22 * 11/18 = 1/2 * 1/2 = 1/4

5/7 * 7 = 35/7 = 5

2/11 * 5 5/6 = 2/11 * 35/6 = 1/11 * 35/3 = 35/33 = 1  2/33