帮我解几道数学的递等式巧算,蟹蟹!要巧算的哦~1、15.72-4.38÷2.42、7.2×2.02÷2.43、9.8×25

1、15.72-4.38÷2.4
=13.895


2、7.2×2.02÷2.4
=7.2÷2.4×2.02
=3×2.02
=6.06


3、9.8×25
=（10-0.2）×25
=10×25-0.2×25
=250-5
=245

1、15.72-4.38÷2.4=15.72-4.38÷0.3÷8=15.72-14.6÷8=15.72-1.7=14.022、7.2×2.02÷2.4=2.4×3×2.02÷2.4=3×2.02×(2.4÷2.4)=6.06×1=6.063、9.8×25=(10-0.2)×25=10×25-0.2×25=250-5=245