1/4*48*2/5
=12*2/5
=4.8
14*2/21+1/2
=4/3+1/2
=11/6
24*(3/2-4-5/4)
=24*3/2-24/4-24*5/4
=36-96-30
=-60-30
=-90
75*11/76
=（76-1）*11/76
=76*11/76-11/76
=11-11/76
=10又65/76