(78.6－0.786×25＋75%×21.4)÷15×1997

(78.6－0.786×25＋75%×21.4)÷15×1997
(78.6－0.786×25＋75%×21.4)÷15×1997

(78.6－0.786×25＋75%×21.4)÷15×1997
原式=（78.6-78.6×0.25+0.75×21.4）÷15×1997
=[78.6×（1-0.25）+0.75×21.4）]÷15×1997
=[78.6×0.75 +0.75×21.4]÷15×1997
=[78.6+21.4]×0.75÷15×1997
=100×0.75÷15×1997
=5×1997
=5×（2000-3）
=5×2000-15
=9985

=((0.786(100-25)+75*0.214)/15*1997
=75/15*1997
=5*1997
=9985