13x-12y=1411x-18y=4
78x-72y=84
44x-72y=16 *(-1)
34x=68
x=2
y=1
4х+3/4-2х+2/4=1
2х+5/4=1
2х=1-5/4
2х=-1/4
х=-1/8
3,21 : 0.3 + 2.42 =10.7 + 2.42 = 13.12
5 : 0.2 - 13 = 25 - 13 = 12
1/4 + 3.17 = 0.25 + 3.17 = 3.42
5/7 + 1/3 + 1/21 = 15/21 + 7/21 - 1/21 = 21/21 = 1
3/5 - 3/8 = 24/40 - 15/40 = 9/40 = 0.225
9/7 : 3/28 = (9 * 28) : (7*3) = 252/21 = 12
2/5 - 0.52 * 5/26 = 0.4 - 2.6/26 = 0.4 -0.1 = 0.3