1) 6/11×4/7. 2) 7/20×10/21. 3) 8/9×27/32. 4) 23/28×49/46. 5) 34/86×43/51. 6) 7/18×90/77. 7) 63/64×48/91. 8) 36/85×34/39

6/11   *  4/7   = (6*4)/(11*7) =  24/77

7/20   * 10/21   =  (7*10)/(20*21) = (1*1)/(2*3) = 1/6

8/9  *  27/32  = (8*27)/(9*32) = (1*3)/(1*4) = 3/4

23/28   * 49/46  = (23 * 49)/(28*46) = (1*7)/(4*2)  = 7/8

34/86  * 43/51   =  (34*43)/(86*51) = (34*1)/(2*51) = 17/51 = 1/3

7/18   * 90/77   = (7*90)/(18*77) = (1*10)/(2*11) = 5/11

63/64 * 48/91  = (63*48)/(64*91) =(7*9*6*8)/(8*8*7*13) =
=(9*3)/(4*13)= 27/52 

36/85   *   34/39 = (36 *34)/(85*39) =  (3*12* 2*17)/(5*17*3*13)=
= (12*2)/(5*13) = 24/65