Question

answer this question no. 10


SOLVE PLEASE

Answer 1

(10).

Given 1st term a = 1.

Last term l = 20.

Sum (sn) = 399.


We know that sum of n terms of an AP is given by:

= > sn = (n/2)(a + l)

= > 399 = (n/2)(1 + 20)

= > 399 * 2 = 21n

= > 798 = 21n

= > n = 38.


Therefore the value of n = 38.



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