6.48-(2.48-1.52)
=6.48-2.48+1.52
=4+1.52
=5.52
45.2-0.7-15.2-8.3
=45.2-15.2-（0.7+8.3）
=30-9
=21
(7+41+74+414+744+4144)×2.5
=（48+488+4888）×2.5
=48×2.5+488×2.5+4888×2.5
=120+1220+12220
=13560