CMA Foundation · Fundamentals of Business Mathematics and Statistics · Arithmetic Progression and Geometric Progression
The first term of an AP is 7 and its common difference is 4. What is the sum of the first 20 terms?
The sum is 900 using S = n/2 × (2a + (n-1)d).
- A880Correct
- B840
- C800
- D920
Explanation
S20 = 20/2 × [2×7 + 19×4] = 10 × (14 + 76) = 10 × 90 = 900? Recheck: 14 + 76 = 90, so S20 = 900. Hence correct value is 900, but compute again with last term: a20 = 7 + 76 = 83; S = 20 × (7+83)/2 = 900.
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