shalini purchased national saving certificate of Rs. 5000 on her daughter's birthday and decided the of Rs 500 on every subsequent birhtday. how much money she will be able to save by her 18th birthday ?

Given: The value of National saving certificate purchased by Shalini on her daughter's birthday = Rs 5000

Then the increased value of certificate in comming years will be Rs (5000 + 500), Rs (5000 + 500 + 500)

Clearly the value of certificates in all years i.e. 5000, 5500, 6000 ........

forms an A.P.

With first term (a) = 5000

and common difference (d) = 500