Saludos Laura. M Pkltz
Respuesta 50%
1. Se definen las variables:
p= precio
c= precio de compra
v = precio de venta
2. Se plantean las ecuaciones de relación:
$$\begin{align}&c=p-(\frac{30}{100} p)\\&\\&c= p*(1-\frac{30}{100} )\\&\\&c= p*(\frac{100-30}{100} )\\&\\&c= p*(\frac{70}{100} )\\&\\&\\&v=p+(\frac{5}{100} p)\\&\\&v=p*(1+\frac{5}{100})\\&\\&v=p*(\frac{100+5}{100})\\&\\&v=p*(\frac{105}{100})\\&\\&\\&ganancia= v-c\\&\\&ganancia=p*(\frac{105}{100}) - p*(\frac{70}{100} )\\&\\&\\&ganancia=p*(\frac{105}{100}) - p*(\frac{70}{100} )\\&\\&\\&ganancia=p*((\frac{105}{100}) - (\frac{70}{100} ))\\&\\&\\&ganancia=p*(\frac{35}{100}) \\&\\&\\&\\&ganancia\ porcentual= \frac{ganancia}{compra}*100\\&\\&\\&\\&ganancia\ porcentual= \frac{p*(\frac{35}{100}) }{ p*(\frac{70}{100} )}*100\\&\\&\\&\\&ganancia\ porcentual= \frac{35}{70}*100\\&\\&\\&ganancia\ porcentual= (0,5)*100\\&\\&\\&ganancia\ porcentual= 50\\&\\&\\&\end{align}$$