SAT Math Multiple Choice Practice Question 219: Answer and Explanation

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Question: 219

21. A sequence begins 1/2, 2, 8, 32, . . . If 1/2 is the first term, 2 is the second term, and 8 is the third term, which of the following expressions represents the nth term?

A. 1/2(2)n-1
B. 1/2(4)n-1
C. 1/2(4)n
D. 2-n
E. 4n

Correct Answer: B


B. Plug numbers in to solve this question. You know that when n is 1 (the first term), the value is 1/2. Check which answer options equal 1/2 when n is 1. (Keep in mind that anything raised to 0 is equal to 1.) Choices (A), (B), and (D) all work. Now, when n is 2, the value should be 2. Check n = 2 in Choices (A), (B), and (D) to see which one equals 2. Choice (A) equals 1, (B) equals 2, and (D) equals 1/4. Choice (B) is the answer.

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