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4 November, 21:59

8. A goldsmith has 130 grams of a gold alloy (a mixture of gold and one or more other metals) containing 85% pure gold. How

much pure gold must be added to this alloy to obtain an alloy that is 90% pure gold?

The amount of pure gold that should be added is

(Type an integer or a decimal.)

grams.

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Answers (1)
  1. 4 November, 22:40
    0
    Answer: 65 grams

    Step-by-step explanation:

    If 130 grams of a gold alloy (a mixture of gold and one or more other metals) containing 85% pure gold, that means the percentage of other metals will be;

    100 - 85 = 15 %

    You should first calculate the amount of gold that makes up this percentage.

    That is, 85% of 130 grams.

    85/100 * 130 = 110.5

    Then, let X be what will be added to the above value to make 90%. So,

    (110.5 + X) / (130 + X) * 100 = 90

    Divide both sides by 100

    (110.5 + X) / (130 + X) = 90/100

    (110.5 + X) / (130 + X) = 0.9

    Cross multiply and open the bracket

    110.5 + X = 117 + 0.9X

    Collect the like terms

    X - 0.9X = 117 - 110.5

    0.1X = 6.5

    Divide both sides by 0.1

    X = 6.5/0.1

    X = 65 grams

    Therefore, the amount of pure gold that should be added is 65 grams
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