JEE Mains · Maths · STD 11 - 8. sequence and series
Let \(S_n\) denote the sum of the first \(n\) terms of an arithmetic progression. If \(\mathrm{S}_{10}=390\) and the ratio of the tenth and the fifth terms is \(15: 7\), then \(S_{15}-S_5\) is equal to :
- A \(800\)
- B \(890\)
- C \(790\)
- D \(690\)
Answer & Solution
Correct Answer
(C) \(790\)
Step-by-step Solution
Detailed explanation
\( \mathrm{S}_{10}=390 \) \( \frac{10}{2}[2 \mathrm{a}+(10-1) \mathrm{d}]=390 \) \( \Rightarrow 2 \mathrm{a}+9 \mathrm{~d}=78 \) \(......(1)\)…
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