利润率=(卖价-进价)/进价;卖价=利润率X进价+进价
卖价不变,设利润率为b,进价为a,则
ab+a=1.3bX0.9a+0.9a
解方程,ab+a=1.17ab+0.9a
0.17ab=0.1a,两边同除以a,解得b=58.82%.