Algebra
Aptitude

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Q.

A man buys Bank's cash certificates every year for a value exceeding the last year's purchase by Rs 400. After 24 years, he finds that the total value of the certificate purchased by him is Rs 144,000. What is the value of the certificates purchased by him in the 13th year?

 A.

Rs 3820

 B.

Rs 5400

 C.

Rs 6200

 D.

Rs 4530

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Solution:
Option(C) is correct

400+800+1200+......144000 (value after 24 years).

We know that, last term

\(=\dfrac{n}{2}[2a+(n-1)d]\)

Where, $a$ is the first term and $d=$ common difference between the term.

Then,

\(144000=\dfrac{24}{2}[2a+(24-1)\times 400]\)

$\Rightarrow  a =$ Rs 1400

Hence, value of the certificates after $13^{th}$ year: 

$=1400+(13−1)×400$

Rs 6200


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