Sequences & Series
Arithmetic Progression (AP)
Grade 11
Question:
<p>(®) If the sum of first 20 terms is same as the sum of first GB) 22 14. If 'r' is taken the larger of its two possible values then the smallest value of n for which S,, exceeds 10 terms in an arithmetic progression then the sum of 15 is- first 30 terms is less than</p>
<p>4</p>
<p>5 + 5 7 199 = a (S) If sum of V2’ 23 34" 9921007 b (4) 20 (6</p>
<p>7</p>
Step-by-Step Solution
Key Concept: Express everything in terms of first term and common difference. That converts a vague-looking progression problem into plain algebra.
Notice that this question is really about the first term and common difference. A clever move here is to parameterize the progression using those two quantities and translate every condition into algebra. Now, we invoke the power of the standard A.P. term and sum formulas, simplify step by step, and confirm the answer as $D$.
Correct Answer: 4