In one alloy there is 12% chromium while in another alloy it is 8%. 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) 8.8 % 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 0.12 * 15 + 0.08 * 35 = 4.6 kg , so the percentage is 4.6 / 50 * 100 = 9.2 % . answer : c .
Answer: C