Question

in an ap if a=1,an=20 and sn=399 then n is​

Answer 1

Sn =n/2(a+an)
399=n/2(1+20)
399=n/2(21)
399*2/21=n
19*2=n
n=38
----------------
Hope se it helps

Answer 2

$\huge \boxed{ \boxed{ \red{ \tt n \: \: = \: \: 38 \: \: terms}}}$

Mark as Brainliest answer please my friend