А) 1/4+5/6 б) 3/20+7/25 в) 2/9+1/6 г) 5/6-3/8 д) 9/10-3/4 е) 3/10-2/15

Найдем значение выражения:

А) 1/4 + 5/6 = (1 * 3 + 5 * 2)/12 = (3 + 10)/12 = 13/12; 

б) 3/20 + 7/25 = (3 * 5 + 7 * 4)/100 = (15 + 28)/100 =  43/100;

в) 2/9 + 1/6 = (2 * 2 + 1 * 3)/18 = (4 + 3)/18 = 7/18; 

г) 5/6 - 3/8 = (5 * 4 - 3 * 3)/24 = (20 - 9)/24 = 11/24; 

д) 9/10 - 3/4 = (9 * 2 - 3 * 5)/20 = (18 - 15)/20 = 3/20; 

е) 3/10 - 2/15 = (3 * 3 - 2 * 2)/30 = (9 - 4)/30 = 5/30 = 5/(6 * 5) = 1/(6 * 1) = 1/6.