a) x + 10/100 * x = 11/10*x
11/10*x + 10/100*11/10*x = 121/100x
121/100*x = 13,31 ⇒ 121x 13,31 * 100 ⇒121x = 1331 ⇒ x = 1331/121 ⇒ x = 11
b) daca 11lei .............. 100%
13,31...............?%
aplicand regula de 3 simpla aflam ca x% = 13,31 * 100/11 ⇒ x% = 1331/11 = 121
13,31 reprezinta 121% din pret deci pretul a crescut cu 21%