А) (5/12 + 3/8)×12/19 =
5/12+3/8 =2 • 5 + 3 • 3/24 = 19/24
19/24×12/19 =19 • 12/24 • 19 = 228/456= 1 • 282 ,282
2•282 , 282 сократим 1/2 =0,5
в)(3 1/4-2 5/7)×(7-6 3/5) = 4/13- 7/ 19 = 7 • 13 - 4 • 19/28 =15/28
7-6 3/5 = 7 - 33/5 = 2/5 = 0,4
15/28×2/5 =2 • 15/5 • 28 = 30/140 = 3 • 10/14 • 10 = 3/14