Выражения 1) 2/5x+4/7x-5/4x; 2)7/12y-3/6y+5/24; 3)5/7m+3/4m-5/8m; 4)11/15c-5/18c-0,4c

1)
2/5x+4/7x-5/4x = 56/140х + 80/140х - 175/140х = -39/140х;

2)
7/12y-3/6y+5/24у = 14/24у - 12/24у + 5/24у = 7/24у;

3)
5/7m+3/4m-5/8m = 40/56m + 42/56m - 35/56m = 47/56m;

4)
11/15c-5/18c-0,4c = 66/90с - 25/90с - 36/90с = 5/90с = 1/18с