Answer :

1 / 4 = ( 1 × 3  ) / ( 3 × 4 ) = 3 / 12 ;
5 / 12 - 1 / 4 = 5 / 12 - 3 / 12 = 2 / 12 = ( 2 ÷ 2 ) / ( 12 ÷ 2 ) = 1 /  6 ;