A grocer has 400 pounds of coffee in stock, 20 percent of which is decaffeinated. If the grocer buys another 100 pounds of coffee of which 70 percent is decaffeinated, what percent, by weight, of the grocer’s stock of coffee is decaffeinated? Select the correct option:
A) 28 %
B) 30 %
C) 32 %
D) 34 %
E) 36 %

Rationale: "1 . 20 % of 400 = 80 pounds of decaffeinated coffee 2 . 70 % of 100 = 70 pounds of decaffeinated coffee 3 . wt have 150 pounds of decaffeinated out of 500 pounds , that means 150 / 500 * 100 % = 30 % . the correct answer is b ."
Answer: B