Question

The first and the last terms of an AP are 10 and 361 respectively. If its common difference is 9 then find the number of terms and their total sum?​

Answer 1

Answer:

Hey mate the answer is

n=40 and S=7420

Refer to the attachment for steps.

Answer 2

Given , first term a = 10

Last term , al = 361

And , common differences , d = 9

Now

al = a+(n-1)

361 = 10 + (n-9)

361 = 10 + 9n - 9

361 = 9n+1

9n = 360

n= 40

Therefore , total number of terms in AP=40

Now , sum of total number of term of an AP is given as :

Sn = n/2 [2a+(n-1)d]

S 40 = 40/2 [2*10+(40-1)9]

= 20(20*351)

= 20*371

=7420

Thus , sum of all 40 terms of AP = 7420

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