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Rohit purchases every year bank certificate of value exceeding the last years purchase by Rs 25.After 20 years, he finds that the total value of the certificate purchased by him is Rs 7250.Find the value of the certificate purchased : (a) In the first year. (b) In the 13th year.
The given situation forms an AP

Let x be the first value.

Then AP will be x, x+25 , x+50 ..........

with a = x and c.d as +25.

Given,

S 20 = 7250

So, Applying formula

7250 = 20/2 ( 2x + 19 * 25)

725 = 2x +475

2x=250

x = 125

i.e Rs.125 in the first year

(ii)  To find a13

a13= a+12d

=125 + 12 * 25

=125 + 300

= 425


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