Вычислите (3/4-1/2)*5 (5/7+1/21):2 (7/10-1/5):3 (1/4-1/12)*5 (1/4+1/6):10 (5/6-1/4):7

(3/4 - 1/2) * 5 = 1/4. 

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

2)  1/4 * 5 = (1 * 5)/(4 * 5) = 5/20 = 1/4. 

(5/7 + 1/21) : 2 = 8/21. 

1). 5/7 + 1/21 = (5 * 3)/(7 * 3) + 1/21 = 15/21 + 1/21 = 16/21; 

2). 16/21 : 2 = 16/21 : 2/1 = 16/21 * 1/2 = (16 * 1)/(21 * 2) = 16/42 = 8/21. 

(7/10 - 1/5) : 3 = 1/6. 

1). 7/10 - 1/5 = 7/10 - (1 * 2)/(5 * 2) = 7/10 - 2/10 = 5/10 = 1/2; 

2). 1/2 : 3 = 1/2 * 1/3 = 1/6. 

(1/4 - 1/12) * 5 = 5/6. 

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

2). 1/6 * 5 = 5/6. 

(1/4 + 1/6) : 10 = 1/24. 

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

2). 5/12 : 10 = 5/12 * 1/10 = 5/120= 1/24. 

(5/6 - 1/4) : 7 = 12. 

1). 5/6 - 1/4 = (5 * 2)/(6 * 2) - (1 * 3)/(4 * 3) = 10/12 - 3/12 = 7/12; 

2). 7/12 : 7 = 7/12 * 1/7 = 12/1 = 12.