TS EAMCET · Maths · Sequences and Series
If the average of the first \(n\) numbers in the sequence \(148,146,144, \ldots\), is 125 , then \(n\) is equal to
- A 18
- B 24
- C 30
- D 36
Answer & Solution
Correct Answer
(B) 24
Step-by-step Solution
Detailed explanation
Given sequence \(148,146,144, \ldots\) and average is 125. \[ \begin{aligned} \therefore \quad S_n & =\frac{n}{2}[2 \times 148+(n-1)(-2)] \quad[\because d=-2] \\ & =\frac{n}{2}[296-2 n+2] \\ & =n[148-n+1]=n[149-n] \end{aligned} \] Hence, \(\quad 125=\frac{n[149-n]}{n}\)…
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