Question

Dupa doua reduceri consecutive de pret, prima de 15%, a doua de 5%, un telefon mobil costa 646 lei. Care a fost pretul initial al telefonului mobil?

Answer 1

I reducere:x-15x/100=x-3x/20=(20x-3x)/20=17x/20
II reducere: 17x/20-5/100·17x/20=17/20-17x/400=(17·20x-17x)/400=
(340x-17x)/400=323x/400
323x/400=646
x=646·400/323
x=800 lei pretul initial
verificare
I reducere:800-800·15/100=800-120=680
II reducere:680-680·5/100=680-34=646