1.原式=(19/4*3/7+19/4*4/7)÷38/3
=19/4(3/7+4/7)÷38/3
=19/4 ÷ 38/3
=3/8
2.(10.5-(5.72+4.28))*16/25
=1/2 * 16/25
=8/25