Question

Find 60 th term of ap -20,-15,-10....... if it has total 60 terms and hence find the sum of last ten term.

Answer 1

Hey Mate ✌

Here's your answer friend,

Given : A.P. ==> -20, -15, -10 ...an

Here, Total terms (n) = 60

first term a = -20

Common difference = (-15)-(-20) = -15 + 20

(d) = 5

==> 60th term = a60 = a + 59d

==> -20 + 59(5) = -20 + 295

==> a60 = 275

Thus, 60th term of the A.P. is 275.


Now, let us invert the A.P.

We get,

==> 295, 290, 285,............-20

==> Now here first term a = 295

==> common difference d = 5

==> last term (L) = (-20)

Now sum of ten terms


Sn = n/2 (a + l)

==> S10 = 10/2 (295 + (-20))

==> S10 = 5 (275)

==> 1375

Thus, sum of last ten terms of the given Arithmetic Progression is 1375.

⭐ Hope it helps you ^_^ ⭐