1) 5 целых 3_4* 3целых 5_7+3 целых 5_7*1 целую 1_4=... (2)

1) 5 3/4 * 3 5/7 + 3 5/7 * 1 1/4 = 26/7 * (23/4 + 5/4) = 26/7 * 28/4 = (26 * 28)/(7 * 4) = 728/28 = 26.
    5 3/4 = (5 * 4 + 3)/4 = 23/4.
    3 5/7 = (3 * 7 + 5)/7 = 26/7.
    1 1/4 =(1 * 4 + 1)/4 = 5/4.
2) 8 3/5 * 6 1/7 - 1 1/7 * 8 3/5 = 43/5 * (43/7 - 8/7) = 43/5 * 35/7 = (43 * 35)/(5 * 7) = 1505/35 = 43.
    8 3/5 = (8 * 5 + 3)/5 = 43/5.
    6 1/7 = (6 * 7 + 1)/7 = 43/7.
    1 1/7 = (1 * 7 + 1)/7 = 8/7.
3) 15 3/8 * 4 1/6 - 4 1/6 * 15 3/8 = 123/8 * (25/6 - 25/6) = 123/8 * 0 = 0.
    15 3/8 = (15 * 8 + 3)/8 = 123/8.
    4 1/6 = (4 * 6 + 1)/6 = 25/6.
4) 10 5/11* 4 1/3 + 10 5/11 * 6 2/3 = 115/11 * (13/3 + 20/3) = 115/11 * 11 = 1265/11 = 115.
    10 5/11 = (10 * 11 + 5)/11 = 115/11.
    4 1/3 = (4 * 3 + 1)/3 = 13/3.
    6 2/3 = (6 * 3 + 2)/3 = 20/3.
5) (6 + 1 1/3 * 2) * 30 =
    1 1/3 = (1 * 3 + 1)/3 = 4/3.
    6 = 5 3/3 = (5 * 3 + 3)/3 = 18/3.
 1. 4/3 * 2 = (4 * 2)/3 = 8/3.
 2. 18/3 + 8/3 = 26/3.
 3. 26/3 * 30 = (26 * 30)/3 = 780/3 = 260.