Вычисли выражения в заданиях 11-20

11. $(7/15) * (8/16) = (7*8)/(15*16) = 56/240 = 7/30$ 12. $(9/10) + (11/12) * (2/9) = (9/10) + (11*2)/(12*9) = (9/10) + (22/108) = (9/10) + (11/54) = (9*54 + 11*10)/(10*54) = (486 + 110)/540 = 596/540 = 149/135$ 13. $39 / (14 - 11/6) = 39 / ((14*6 - 11)/6) = 39 / ((84 - 11)/6) = 39 / (73/6) = (39*6)/73 = 234/73$ 14. $24/49 : 7 + 6/7 + 1/14 = 24/(49*7) + 6/7 + 1/14 = 24/343 + 6/7 + 1/14 = (24*2 + 6*98 + 1*49) / 686 = (48 + 588 + 49)/686 = 685/686$ 15. $5/6 + 4/9 : 16/21 = 5/6 + (4/9)*(21/16) = 5/6 + (4*21)/(9*16) = 5/6 + 84/144 = 5/6 + 7/12 = (5*2 + 7)/12 = (10 + 7)/12 = 17/12$ 16. $8/9 - 3/8 * 27/28 = 8/9 - (3*27)/(8*28) = 8/9 - 81/224 = (8*224 - 81*9) / (9*224) = (1792 - 729) / 2016 = 1063/2016$ 17. $16/21 : 12/35 - 2 = (16/21) * (35/12) - 2 = (16*35)/(21*12) - 2 = 560/252 - 2 = 20/9 - 2 = (20 - 2*9)/9 = (20 - 18)/9 = 2/9$ 18. $35/24 * 15/32 - 3 = (35*15)/(24*32) - 3 = 525/768 - 3 = 175/256 - 3 = (175 - 3*256) / 256 = (175 - 768)/256 = -593/256$ 19. $15/2 - 10/28 : 21 = 15/2 - 10/(28*21) = 15/2 - 10/588 = 15/2 - 5/294 = (15*147 - 5)/294 = (2205 - 5)/294 = 2200/294 = 1100/147$ 20. $18/81 : 5/2 - 2/3 = (18/81) * (2/5) - 2/3 = 36/405 - 2/3 = 4/45 - 2/3 = (4 - 2*15)/45 = (4 - 30)/45 = -26/45$