Question

Dupa doua ieftiniri succesive de cate 10% un dictionar costa 121,50 lei.Aflati pretul initial

Answer 1

[100-10]/100 ·y=z; [100-10]/100 ·z=121,5lei;
⇒90/100 ·z=121,5
⇒90/100 ·z=1215/10
⇒9/10 ·z=1215/10
⇒z=1215/10/9/10
⇒z=1215/10·9/10
⇒z=243/10·9/2
⇒z=2187/20⇒z=109,35[lei];
⇒90/100 ·y=109,35
⇒90/100 ·y=10935/100
⇒y=10935/100/90/100
⇒y=10935/100·90/100
⇒y=2187/10·9/10
⇒y=19683/100⇒y=196,83[pretul initial];

Answer 2

121.5x10%=121.50+12.15=133.72
133.72x10%=133.72+13.72=147.09pretul initial