7х+4у=5|×2
3х+2у=3|×-4
14х+8у=10
12х-8у=-12
26х=-2|÷-2
х=-13
3х+2у=3
3×(-13)+2у=3
-39+2у=3
2у=3+39
2у=42|÷2
у=21
3 двойки и 10 пятерок,
18/6=3 двойки
15/3=5(берем две)
5+5=10 пятерки
А) 1 - 4/9 = 1/1 - 4/9 = 9 - 4/9 = 5/9
б) 8 8/15 - 4 9/20 = 128/15 - 89/20 = 512 - 267/60 = 245/60 = 49/12
в) 4/1 - 3 3/4 = 4/1 - 15/4 = 16 - 15/4 = 1/4
г) 9 4/21 - 4 11/14 = 193/21 - 67/14 = 386 - 201/42 = 185/42
д) 7 1/10 - 3 1/6 = 71/10 - 19/6 = 213 - 95/30 = 118/30 = 59/15
е) 5 5/33 - 4 1/2 = 170/33 - 9/2 = 340 - 297/66 = 43/66
Пусть неизвестное будет х тогда
х+56=99
х=99-56
х=33