(21.5-21)*25*0.5+25*0.4 等于多少
= 0.5 x 25 x 0.5 + 25 x0.4
= 25 x 0.25 +25 x 0.4
= 25 x (0.25+0.4)
= 25 x 0.65
= 65 x 0.25
= 65 ÷4
= 16.25