Номер 538 Вычислите: 1)5/9+3/4; 2)4/9+11/15; 3)1/9-10/99; 4)5/6-3/4; 5)5/8+7/9; 6)7/30+11/36; 7)8/11-5/12; 8)8/11-5/

1) 5/9 + 3/4 = 20/36 + 27/36 = (20 + 27)/36 = 

= (36 + 11)/36 = 1 11/36;

2) 4/9 + 11/15 = (4 * 5)/(9 * 5) + (11 * 3)/(15 * 3) = (20 + 33)/45 =

= (45 + 8)/45 = 1 8/45;

3) 1/9 - 10/99 = (11 * 1)/(9 * 11) - 10/99 = 1/99;

4) 5/6 - 3/4 = 10/12 - 9/12 = (10 - 9)/12 = 1/12;

5) 5/8 + 7/9 = (5 * 9)/(8 * 9) + (7 * 8)/(8 * 9) = (45 + 56)/72 =

= (72 + 29)/72 = 1 29/72;

6) 7/30 + 11/36 = 7/(5 * 6) + 11/(6 * 6) =

= (7 * 6)/(30 * 6) + (11 * 5)/(36 * 5) = (55 + 42)/180 = 97/180;

7) 8/11 - 5/12 = 96/(11 * 12) - 55/(12 * 11) =

= (96 - 55)/132 = 41/132;

8) Здесь будет отрицательное значение.

8/11 - 5 = 8/11 - 55/11 = - 47/11 = - 4 3/11.

Задачка 545.

1) 1/5 + 1/10 + 1/15 = 6/30 + 3/30 + 2/30 = 11/30.

2) 1 - 11/30 = 30/30 - 11/30 = 19/30.

Ответ: выполнено 11/30, осталось 19/30.

Задача 546*.

1 поезд проходит 1/26 часть пути.

2 поезд - 1/36.

За 6 минут произойдет сближение на:

6 * (1/26 + 1/36) = 6/26 + 6/36 = 3/13 + 1/6 = 18/78 + 13/78 = 31/78.