Вычислите значение выражений 1)-1/4+3/5 2)9/11+(-2/5) 3)-20/21+3/7 4)-8 9/14+3 3/ 5)7 5/12+(-3

Приведем дроби к общему знаменателю и вычислим значение выражения:

1) -1/4 + 3/5 = -5/20 + 12/20 = (-5 + 12)/20 = 7/20;

2) 9/11 + (-2/5) = (9 * 5)/55 + (-2 * 11)/55 = 45/55 - 22/55 = (45 - 22)/55 = 23/55;

3) -20/21 + 3/7 = -20/21 + (3 * 3)/21 = -20/21 + 9/21 = (-20 + 9)/21 = -11/21;

4) -8 9/14 + 3 3/7 = -8 + 3 - 9/14 + 3/7 = -5 - 9/14 + 6/14 = -5 - 3/14 = -5 3/14;

5) 7 5/12 + (-3 7/24) = 7 - 3 + 5/12 - 7/24 = 4 + 10/24 - 7/24 = 4 + 3/24 = 4 + 1/8 = 4 1/8;

6) -6 11/12 + (-8 13/18) = -6 - 8 - 11/12 - 13/18 = -14 - 33/36 - 26/36 = -14 - 59/36 = -14 - 1 23/36 = -15 23/36.