(1,25 : 1 7/8) / (1 5/6 - 1 3/4)*2,4 = 3 1/3,
числитель:
1) 1,25 : 1 7/8 = 125/100 : 15/8 = 125/100 * 8/15 = 5/4 * 8/15 = 2/3,
знаменатель:
2) 1 5/6 - 1 3/4 = 11/6 - 7/4 = 22/12 - 21/12 = 1/12,
3) 1/12 * 2,4 = 1/12 * 24/10 = 2/10 = 1/5,
4) 2/3 : 1/5 = 2/3 * 5/1 = 10/3 = 3 1/3