A) 35
B) 36
C) 37
D) 40
Correct Answer: A
Solution :
We have \[\frac{3+5+7+......\text{upto}\ n\ \text{terms}}{5+8+11+........\text{upto}\ 10\ \text{terms}}=7\] \[\Rightarrow \frac{\frac{n}{2}[6+(n-1)2]}{\frac{10}{2}[10+(10-1)3]}=7\Rightarrow \frac{n(2n+4)}{10\times 37}=7\] \[\Rightarrow \]\[{{n}^{2}}+2n-1295=0\Rightarrow (n+37)(n-35)=0\] Hence\[n=35\].
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