===== Testing multiply and mixed =====
2/3 * 1/6 = 1/9 ==> 1/9
1/5 * 4/9 = 4/45 ==> 4/45
3/7 * 12/21 = 12/49 ==> 12/49
5/8 * 3/16 = 15/128 ==> 15/128
7/8 * 3/12 = 7/32 ==> 7/32
0/8 * 3/16 = 0/1 ==> 0
1/1 * 3/16 = 3/16 ==> 3/16
5/8 * -3/16 = -15/128 ==> -15/128
1/5 * -4/9 = -4/45 ==> -4/45
-1/5 * -4/9 = 4/45 ==> 4/45
5/5 * 5/5 = 1/1 ==> 1 
0/4 * 5/7 = 0/1 ==> 0
0/0 * 0/0 = 0/0 ==> 0