(6целых1/4-4целых1/8)×4+3целых1/3: 2целых1/3

) 
1/12 + 1/6 = 1/12 + 2/12 = 3/12 = 1/4 
3/8 - 1/4 = 3/8 - 2/8 = 1/8 
1/4:1/8 = 8/4 = 2 
ответ: 2 
2) 
7/9 - 2/3 = 7/9 - 6/9 = 1/9 
1/3 + 2/15 = 5/15 + 2/15 = 7/15 
1/9 : 7/15 = 15 / 63 = 5/21 
ответ: 5/21 
3) 
5/7 - 2/3 = 15/21 - 14/21 = 1/21 
4/9 - 5/12 = 16/36 - 15/36 = 1/36 
1/21 : 1/36 = 36/21 = 12/7 
ответ: 12/7 
4) 
1 - 7/10 = 10/10 - 7/10 = 3/10 
2 + 1/4 = 8/4 + 1/4 = 9/4 
3/10 * x = 9/4 
x = 9/4 : 3/10 = 90/12 = 15/2 = 7,5 
5) 
3 + 1/8 + 1 + 3/4 = 4 + 1/8 + 3/4 = 32/8 + 1/8 + 6/8 = 39/8 
2 + 1/6 = 12/6 + 1/6 = 13/6 
39/8 * x = 13/6 
x = 13/6 : 39/8 
x = (13*8) / (6*39) = 8 / (6*3) = 4/9