narendre u r mistaking in ur basic calculation....

u wrote 2544(x^2)=25.44 lacs = 2544000

that give x^2 = 1000

and now because actual price of the diamond is (65x)^2=4225*x^2

given x^2=1000 which gives price to be 4225000 = 42.25 lacs

hope u understood......