Question

A mixture of 30 pounds of candy sells for $1.10 a pound. The mixture consists of chocolates worth $1.50 a pound and chocolates worth 90¢ a pound. How many pounds of the $1.50 chocolate were used to make the mixture?
A)15
B)10
C)12

Answer 1

$x-chocolate\ worth\ 1,50\ \ per\ pound\\ y-chocolate\ worth\ 0,9\ \ per\ pound\\ \\\\ \left \{ {{x+y=30} \atop {30*1,10=x*1,50+y*0,9}} \right.\\\\ \left \{ {{x=30-y} \atop {33=1,5x+0,9y}} \right. \\\\ Using \ substitution\ method:\\\\33=1,5(30-y)+0,9y\\\\ 33=45-1,5y+0,9y\\\\ -12=-0,6y\ |:-0,6\\\\ y=20\\ x=10$