As if one variable weren't enough, the ACT Math exam will sometimes throw multiple variables into some of its algebra questions. The following practice questions test your skills with using substitution to solve for the variables a and b, and rearranging an equation to solve it in terms of yx.

Practice questions

  1. If a is five greater than b, and the sum of a and b is –15, then b2 =

    A. 100 B. 64 C. 25 D. 20 E. 0

  2. If
    then yx =

Answers and explanations

  1. The correct answer is Choice (A).

    Set up equations from the wording of the question: a = 5 + b and a + b = –15. Substitute the value of a in the first equation for a in the second equation and solve for b:


    So b2 = 100.

  2. The correct answer is Choice (D).

    Get the terms that have y and x in them on one side and all the terms that have nothing to do with y and x on the other side:


About This Article

This article is from the book:

About the book authors:

Lisa Zimmer Hatch, MA, and Scott A. Hatch, JD, have been helping students excel on standardized tests and navigate the college admissions process since 1987. They have written curricula and taught students internationally through live lectures, online forums, DVDs, and independent study.

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