In one alloy there is 10% chromium while in another alloy it is 6%. 15 kg of the first alloy was melted together with 35 kg of the second one to form a third alloy. Find the percentage of chromium in the new alloy.
Choose the correct choice from the following answers.
A) 7.2 %
B) 9 %
C) 9.2 %
D) 8.6 %
E) 8.4 %

Rationale: "the amount of chromium in the new 15 + 35 = 50 kg alloy is 0.10 * 15 + 0.06 * 35 = 3.6 kg , so the percentage is 3.6 / 50 * 100 = 7.2 % . answer : a ."
Answer: A