30%=1.3對應100%-30% = 70% = 0.70;
10%=1.1對應100%-10% = 90% = 0.90;
從10元的進價中贏30%,即10*1.30=13元;
從買入價10元到向下虧損10%止損,就是10 * 0.9 = 9元。