3/4 x 8/9 x 15/16 x ...... x 99/x100
=(1 x 3) x (2 x 4) x (3 x 5) x (4 x 6) x (6 x 7) x (7 x 8) .... x (9 x 11)
(2 x 2) x (3 x 3) x (4 x 4) x (5 x 5) x (6 x 6) x ( 7 x 7) x ..... x (10 x 10)
= (1 x 2 x 3 x 4 x 5 x ... x 9) x (3 x 4 x 5 x 6 x 7 x .... 11)
(2 x 3 x 4 x .......... x 10) x ( 2 x 3 x 4 x 5 x 6 x 7 x .... 10)
=( 1x 11):( 10 x 2)
= 11
20