Practice Quiz

SAT Math

Category - Number and Operations

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What is the 45th element in the arithmetic sequence -9,-6,-3,0,3,6…?
  1. 112
  2. 123
  3. 132
  4. 143
  5. 154
Explanation
Answer: B - The 45th element in the sequence is 123.
a_1 = -9,d = 6-3 = 3,n = 45
a_n = a_1 + (n-1)d = -9 + (45-1)×3 = -9 + 44×3 = -9 + 132 = 123
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