5/7 x 1/4 + 3/4 x 5/7
= 5/7 x (1/4 + 3/4)
= 5/7 x 1
= 5/7
或
5/7 x 1/4 + 3/4 x 5/7
= 5/7 x 1/4 x (1 + 3)
= 5/28 x 4
= 5/7
5/7×1/4+3/4×5/7=5/7(1/4+3/4)=5/7x1=5/7
5/7x1/4+3/4x5/7
=5/7x(1/4+3/4)
=5/7x1
=5/7
5/7×1/4+3/4×5/7
=5/28+15/28
=20/28
=5/7