Вынесите общий множитель за скобки: 1/4*12/25+5/6*12/25; 15/28*2/3-15/28*1/5; 1/8*4/11-1/10*4/11+1/4*4/11; 18/49*1/3-18/49*1/9+1/6*18/49;

1/4*12/25+5/6*12/25=12/25 * (1/4 + 5/6); 
15/28*2/3-15/28*1/5 = 15/28 * (2/3 - 1/5);
1/8*4/11-1/10*4/11+1/4*4/11 = 4/11 * (18 - 1/10 + 1/4);
18/49*1/3-18/49*1/9+1/6*18/49 = 18/49 * (1/3 - 1/9 + 1/6);