Question

Pavel a cheltuit 2\5 din suma pe care a avut-o in prima zi.A doua zi a cheltuit o jumatate din rest.Ce suma a avut initial daca iau ramas 15 lei.Cat a cheltuit a doua zi?Va rog!!!

Answer 1

Notam cu s suma initiala

$\frac{2}{5}s+\frac{1}{2}(s-\frac{2}{5}s)+15=s$

Primul termen al ecuatiei reprezinta cat a cheltuit in prima zi.
Al doilea termen al ecuatiei reprezinta cat a cheltuit in a doua zi.
Ultimul termen reprezinta cat i-a ramas.
In total ne da suma initiala.
Rezolvam ecuatia si ne da s=50.

Answer 2

prima zi⇒2/5 ·x=2x/5;
a ramas x-2x/5=5x/5-2x/5=3x/5;
a doua zi⇒3x/5·1/2=3x/10;
a ramas 3x/5-3x/10=6x/10-3x/10=3x/10;
⇒3x/10=15⇒x=10·15/3⇒x=10·5⇒x=50[lei-suma initiala];
a doua zi⇒3·50/10⇒3·5=15[lei];