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Strategy 9: Estimate

Sometimes it is not necessary to perform extensive calculations to solve a problem — it is sufficient to estimate the answer. The degree of accuracy needed depends on the particular question being asked. Care should be taken to determine how far off your estimate could possibly be from the actual answer to the question. Estimation can also be used to check whether the answer to a question is reasonable.

• This strategy is used in the following two sample questions.

This is a Quantitative Comparison question.

  1. Quantity A Quantity B
    54% of 360 150

    (A) Quantity A is greater.
    (B) Quantity B is greater.
    (C) The two quantities are equal.
    (D) The relationship cannot be determined from the information given.



    Without doing the exact computation, you can see that 54 percent of 360 is greater than One half of 360, which is 180, and 180 is greater than Quantity B, 150. Thus, the correct answer is Choice A, Quantity A is greater.

This is a Multiple-Choice – Select One Answer Choice question.

  1. A car got 33 miles per gallon using gasoline that cost $2.95 per gallon. Approximately what was the cost, in dollars, of the gasoline used in driving the car 350 miles?

    (A) $10
    (B) $20
    (C) $30
    (D) $40
    (E) $50



    Scanning the answer choices indicates that you can do at least some estimation and still answer confidently. The car used 350 over 33 gallons of gasoline, so the cost was Open parenthesis, 350 over 33, close parenthesis, times 2.95 dollars. You can estimate the product Open parenthesis, 350 over 33, close parenthesis, times 2.95 by estimating 350 over 33 a little low, 10, and estimating 2.95 a little high, 3, to get approximately 10 times 3 = 30 dollars. You can also use the calculator to compute a more exact answer and then round the answer to the nearest 10 dollars, as suggested by the answer choices. The calculator yields the decimal 31 point two, eight, seven, dot, dot, dot. which rounds to 30 dollars. Thus, the correct answer is Choice C, $30.