Practice Test

Question 2 • Algebra: Concepts and Connections

Which two expressions are both equivalent to t , the total number of grams of silver in the mixture?

Answer

15 times 0 point 7 5 and 0 point 7 open paren 15 minus x close paren 0 point 9

15 plus 0 point 7 5 and 0 point 7 open paren 15 minus x close paren 0 point 9 x

15 plus 0 point 7 5 and 0 point 7 times open paren 15 minus x close paren plus 0 point 9 x

15 times 0 point 7 5 and 0 point 7 times open paren 15 minus x close paren plus 0 point 9 x

Explanation

The original 15-gram mixture contains 75% silver, so its silver amount is 15 × 0.75. In the new mixture, 15 − x grams contain 70% silver and x grams contain 90% silver, giving 0.7(15 − x) + 0.9x. Choice D gives both expressions; using addition instead of multiplication in either expression would not calculate the silver amounts correctly.

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