SAT Math Multiple Choice Practice Question 112: Answer and Explanation

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Question: 112

2. A sequence of numbers is created by starting with k, and then adding 3 to the previous number to create each new number. If the 20th number in this sequence is 55, then k equals

A. -5
B. -2
C. 1
D. 5
E. 35

Correct Answer: B

Explanation:

B. By the time you get to the 20th number, you've added three 19 times (not 20). Thus, you've added 19 × 3 = 57. Because you're now at 55, you must have started at 55 - 57 = -2.

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