Найдите значение выражений 1/2-1/4+2/5 3/4-1/2+7/8 1/3-1/9+1/6 5/6-2/3+1/4

 1/2 - 1/4 + 2/5 = 13/20. 

1). 1/2 - 1/4 = (1 * 2) / (2 * 2) - 1/4 = 2/4 - 1/4 = (2 - 1) / 4 = 1/4; 

2). 1/4 + 2/5 = (1 * 5) / (4 * 5) + (2 * 4) / (5 * 4) = 5/20 + 8/20 = (5 + 8) / 20 = 13/20. 

3/4 - 1/2 + 7/8 = 1 1/8.

1). 3/4 - 1/2 = 3/4 - (1 * 2) / (2 * 2) = 3/4 - 2/4 = (3 - 2) / 4 = 1/4; 

2). 1/4 + 7/8 = (1 * 2) / (4 * 2) + 7/8 = 2/8 + 7/8 = (2 + 7) / 8 = 9/8 = 1 1/8. 

1/3 - 1/9 + 1/6 = 7/18. 

1). 1/3 - 1/9 = (1 * 3) / (3 * 3) - 1/9 = 3/9 - 1/9 = 2/9;

2). 2/9 + 1/6 = 4/18 + 3/18 = 7/18.

5/6 - 2/3 + 1/4 = 5/12. 

1). 5/6 - 2/3 = 5/6 - 4/6 = 1/6; 

2). 1/6 + 1/4 = 2/12 + 3/12 = 5/12.