4×0.27×25
=0.27×4×25
=0.27×100
=27;
3.8×99＋3.8
=3.8×(1+99)
=3.8×100
=380;
（8＋4/9）÷4
=2+1/9
=19/9;
2/5＋3/7＋3/5＋4/7
=(2/5+3/5)+(3/7+4/7)
=1+1
=2;