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Mixtures & Alligation · Question 24 of 60

Question 24

MediumOriginal question

A goldsmith has 22-carat gold and 18-carat gold. She wants to make 60 g of 21-carat gold. How many grams of 18-carat gold should she use?

Options for question 24

Show the answer and explanation
CorrectNot quiteAnswer A

Correct answer: A

Explanation

  1. 22-carat : 18-carat = (21−18):(22−21)=3:1(21 - 18) : (22 - 21) = 3 : 1.

  2. 18-carat gold = 14×60=15\frac{1}{4} \times 60 = 15 g.

Worth noting

45 g is the 22-carat part. The target 21 is much closer to 22, so most of the mix must be 22-carat.

Concept
Alligation applied to purity (carats)
Typical time
60 s
Your time
—
The rule this testsThe alligation rule
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