Вычислите: 3/5+1/5, 2/7+1/3, 3/4+5/12, 2/25+1/20; 3/7-2/7, 11/12-2/3, 2/3-5/9, 5/21-3/14

Вычислим значение каждого выражения, где нужно приведем к общему знаменателю:

1) 3/5 + 1/5 = (3 + 1)/5 = 4/5;

2) 2/7 + 1/3 = (2 * 3 + 1 * 7)/21 = (6 + 7)/21 = 13/21;

3) 3/4 + 5/12 = (3 * 3 + 5)/12 = (9 + 5)/12 = 14/12 = 1 2/12 = 1 1/6;

4) 2/25 + 1/20 = (2 * 4 + 1 * 5)/100 = (8 + 5)/100 = 13/100;

5) 3/7 - 2/7 = (3 - 2)/7 = 1/7;

6) 11/12 - 2/3 = (11 - 2 * 4)/12 = (11 - 8)/12 = 3/12 = 1/4;

7) 2/3 - 5/9 = (2 * 3 - 5)/9 = (6 - 5)/9 = 1/9;

8) 5/21 - 3/14 = (5 * 2 - 3 * 3)/42 = (10 - 9)/42 = 1/42.