(2/7+3 1/2)*4 2/3= (2/7+7/2)*14/3= (4/14+49/14)*14/3= 53/14*14/3=53/3=17 2/3
(4 1/5-2 3/4)*2 2/19= (21/5-11/4)*40/19= (84/20-55/20)*40/19= 29/20*40/19=58/19= 3 1/19
(5 6/7+3 5/21)*2 1/10= (41/7+68/21)*21/10= 123/21+68/21)*21/10= 191/21*21/10= 191/10= 19 1/10