（78.6-0.786×25十75%×21.4）÷15×2011=（78.6-78.6×0.25+75%×21.4）÷15×2011，=[（1-0.25）×78.6+0.75×21.4]÷15×2011，=[0.75×78.6×0.75×21.4]÷15×2011，=（78.6+21.4）×0.75÷15×2011，=100×0....