1) (5/7) x (7/12) ÷ (5/16)
= (35/84) ÷ (5/16)
= (35/84) x (16/5)
= (560/420)
= 4/3

2) (9/10) ÷ (5/11) ÷ (5/16)
= (9/10) x (11/5) ÷ 5/16
= (99/50) ÷ (5/16)
= (99/50) x (16/5)
= 792/250
= 1584/500
= 79/25

3) (2/9) x (3/7) ÷ (5/21)
= (6/63) ÷ (5/21)
= (6/63) x (21/5)
= 126/315
= 42/105
= 6/15
= 2/5

4) (7/25) ÷ (3/10) x (5/6)
= (7/25) x (10/3) x (5/6)
= (70/75) x (5/6)
= (14/15) x (5/6)
= 70/90
= 7/9