1) 7/12 + 7/20 = (7 * 5 + 7 * 3)/60 = (35 + 21)/60 = 56/60 = 14/15;
ответ: 14/15.
2) 3/8 + 1/18 = (3 * 9 + 1 * 4)/72 = (27 + 4)/72 = 31/72;
ответ: 31/72.
3) 1/12 + 11/14 = (1 * 14 + 11 * 12)/168 = (14 + 132)/168 = 146/168 = 73/84;
ответ: 73/84.
4) 2/15 - 7/12 = (2 * 4 - 7 * 5)/60 = (8 - 35)/60 = -27/60 = -9/20;
ответ: - 9/20.
5) 9/14 - 5/12 = (9 * 12 - 5 * 14)/168 = (108 - 70)/168 = 38/168 = 19/84;
ответ: 19/84.
6) 19/75 + 7/50 = (19 * 2 + 7 * 3)/150 = (38 + 21)/150 = 59/150.
ответ: 59/150.
