Maths · Arithmetic and Geometric progressions
Find the common difference of an AP. whose first term is 100 and the sum of whos
Find the common difference of an AP. whose first term is 100 and the sum of whose first six terms is five times the sum of the next six terms.
- A. 10
- B. -10
- C. 5 \)
- D. - 5
Step-by-step solution
Let a=100 and common difference d. S_6 = 600+15d, sum of next six terms = S_12 - S_6 = 600+51d. Given S_6 = 5*(sum of next six), so 600+15d = 3000+255d => -240d=2400 => d=-10.
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