11. 50% + 3/5 : 0,75

= 50/100 + (3/5 : 75/100)

= 3/5 x 100/75

= 300/375

= 50/100 + 300/375

= 750/1500 + 1200/1500

= 1950/1500

= 1 450/1500

12. (3/4 – 25%) x 6/5

= 3/4 – 25/100

= 75/100 – 25/100

= 50/100 x 6/5

= 300/500

= 3/5

13. 4,2 – (2 4/5 + 60%)

= 420/100 – (2 4/5 + 60/100)

= 14/5 + 60/100

= 280/100 + 60/100

= 340/100

= 420/100 – 340/100

= 80/100

= 8/10

14. 1/4 : 20% + 1,35

= (1/4 : 20/100) + 135/100

= 1/4 x 100/20

= 100/80 + 135/100

= 500/400 + 540/100

= 1040/400

= 2 240/400

15. 1,4 : 7/2 + 30% x 2 2/3

= (14/100 : 7/2) + (30/100 x 8/3)

= 14/100 x 2/7

= 28/700

= 30/100 x 8/3

= 240/300

= 28/700 + 240/300

= 84/2100 + 1680/2100

= 1764/2100

= 21/25