(2 целых 3/5 - 5/8) : 19 целых 3/4 = ?

(2 3/5 - 5/8) : 19 3/4 = 1/10

1) 2 3/5 - 5/8 = 2 24/40 - 25/40 = 1 64/40 - 25/40 = 1 целая 39/40
2) 1 39/40 : 19 3/4 = 79/40 : 79/4 = 79/40 * 4/79 = 4/40 = 1/10 = 0,1

Пояснения:
3/5 = 24/40 - доп.множ. 8
5/8 = 25/40 - доп.множ. 5
1 целая 39/40 = (1*40+39)/40 = 79/40
19 целых 3/4 = (19*4+3)/4 = 79/4

Вот, думаю, разберешь