Q1 of 69 Page 78

On 1st Jan 2016, Sanika decides to save ₹ 10, ₹ 11 on second day, ₹ 12 on third day. If she decides to save like this, then on 31st Dec 2016 what would be her total saving?

By given information we can form an A.P.

10, 11, 12, 13, ……


Hence, the first term a = 10


Second term t1 = 11


Third term t2 = 12


Thus, common difference d = t2 – t1 = 12 – 11 = 1


Here, number of terms from 1st Jan 2016 to 31st Dec 2016 is,


n = 366


We need to find S366


Now, By using sum of nth term of an A.P. we will find it’s sum



Where, n = no. of terms


a = first term


d = common difference


Sn = sum of n terms


Thus, on substituting the given value in formula we get,



⇒S366 = 183 [ 20 + 365]


⇒S366 = 183 × 385


⇒S366 = Rs 70,455


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