2.4-2.4*4/7-3/7
=2.4×(1-4/7)-3/7
=2.4×3/7-3/7
=3/7(2.4-1)
=3/7×1.4
=0.6
24/25*24
=24/25×(25-1)
=24-24/25
=23又1/25