Question

Dupa 2 reduceri consecutive de pret,ambele de 10%,un calculator costa 972 lei.Care a fost pretul initial al calculatorului?

Answer 1

x = pret
 x -  10%·x = x· ( 1 - 10 /100 ) = x · ( 1 - 1 /10 ) =x ·( 10 -1) /10 = 9·x /10 
9x /10  - 10% · 9·x /10 = 9·x·[ 1  - 10 / 100 ] / 10   = 9·x·[ 1 -1 /10 ] / 10 
= 9 ·x · [10 -1 ]  /10·10 = 9· 9·x / 100 
81·x / 100 = 972 
x = 972 · 100 : 81 x 
 x = 12 · 100 =1200 lei