Math, asked by ojas1k, 1 month ago

in an a.p. 1st term is 1 and the last term is 20. the sum of all terms is 399 then n = ?

Answers

Answered by rizwan1

3

Step-by-step explanation:

Sn = n / 2[ a + a+ ( n- 1)d ] =399

399 = n/2 [ 21]

n = (399×2)/21 = 38

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