Сделайте деянье: a)6 7/15-3 11/20;б)4 10/27+2 13/18;в)13 1/14-(3 5/21+4 6/7)

a) 6 7/15 - 3 11/20 = 35/12 = 2 11/12.
    6 7/15 = (6 * 15 + 7)/15 = 97/15.
    3 11/20 = (3 * 20 + 11)/20 = 71/20.
    388/60 - 213/60 = 175/60 сократим на 5 = 35/12 = 2 11/12.
б) 4 10/27 + 2 13/18 = 7 5/54.
    4 10/27 = (4 * 27 + 10)/27 = 118/27.
    2 13/18 = (2 * 18 + 13)/18 = 49/18.
    236/54 + 147/54 = 383/54 = 7 5/54.
в) 13 1/14 - (3 5/21 + 4 6/7) = 4 41/42.
    13 1/14 = (13 * 14 + 1)/14 = 183/14.
    3 5/21 = (3 * 21 + 5)/21 = 68/21.
    4 6/7 = (4 * 7 + 6)/7 = 34/7.
 1. 68/21 + 102/21 = 170/21.
 2. 549/42 - 340/42 = 209/42 = 4 41/42.