Vlad cheltuieste 25% dintr-o suma de bani,apoi trei cincimi din rest,ramanandui 240lei .Ce suma a avut initial Vlad?

Notam cu S suma de bani initiala pe care a avut-o Vlad, iar r restul.
Calculam 25/100 * S + 3/5 * r = 240 <=> S/4 + 3r/5 = 240
 

Notam x suma de bani initiala!

[tex] \frac{100x}{100} [/tex]-[tex] \frac{25x}{100} [/tex]  =  [tex] \frac{75x}{100} [/tex] suma ramasa

[tex] \frac{75x}{100} [/tex]*[tex] \frac{3}{5} [/tex] = [tex] \frac{225}{500} [/tex] = [tex] \frac{45x}{100} [/tex] a cheltuit a doua oara

[tex] \frac{75x}{100} [/tex]-[tex] \frac{45x}{100}[/tex] = [tex] \frac{30x}{100} [/tex] = 240 lei <=> 30x=24000 <=> x = 800 lei

Vlad a avut initial 800 lei...