①24× 1 8 ÷ 1 3 =3÷ 1 3 =9；② 2 7 ÷（ 4 5 - 2 3 ）= 2 7 ÷ 2 15 =2 1 7 ；③40÷ 2 3 ×80%=60×0.8=48；答：①乙数是9；②这个数是2 1 7 ；③这个数的80%是48．
