Найдите значение выражений. а) (3/15+7/20)*25 б) 12 2/9*3 в) (5 5/12-3

а) (3/15 + 7/20) * 25 = 13 3/4 = 13,75;

1) 3/15 + 7/20 = 12/60 + 21/60 = (12 + 21)/60 = 33/60 = 11/20;

2) 11/20 * 25 = 11 * 25/20 = 11 * 5/4 = 55/4 = 13 3/4 = 13,75;

б) 12 2/9 * 3 = 110/9 * 3 = 110 * 3/9 = 110 * 1/3 = 110/3 = 36 2/3;

в) (5 5/12 - 3 1/24) * 24 = 57;

1) 5 5/12 - 3 1/24 = 65/12 - 73/24 = 130/24 - 73/24 = (130 - 73)/24 = 57/24 = 19/8 = 2 3/8;

2) 2 3/8 * 24 = 19/8 * 24 = 19 * 24/8 * 1 = 19 * 3/1 * 1 = 57/1 = 57;

г) 2/9 * 1/16 + 7/9 * 1/16 = 1/16 * (2/9 + 7/9) = 1/16;  

1) 2/9 + 7/9 = 9/9 = 1;

2) 1/16 * 1 = 1/16;