A jeweller melts together two alloys containing 70% gold and 85% gold in the ratio $1 : 2$ by weight. What percentage of the new alloy is gold?

75%Correct answerYour answer77.5%Correct answerYour answer80%Correct answerYour answer82.5%Correct answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer C

Correct answer: C

Gold in 3 units = $1 \times 70\% + 2 \times 85\% = 70 + 170 = 240$ (percent-units).
Gold percentage = $\frac{240}{3} = 80\%$ .

Worth noting

77.5% is the simple average; 75% attaches the larger weight to the 70% alloy.

Ten questions from Mixtures & Alligation, at your own pace.

Ten questions from Mixtures & Alligation, at your own pace.

A jeweller melts together two alloys containing 70% gold and 85% gold in the ratio 1:21 : 21:2 by weight. What percentage of the new alloy is gold?