Question

i need the question now..........

Answer 1

a+(n-1)d=An
1+(n-1)d=20
(n-1)d=20-1
(n-1)d=19.....1eq

Sn=n/2(a+l)
399=n/2(1+20)
399=21n/2
798=21n
n=38.....2eq

put 2eq in 1eq
we get
(38-1)d=19
37d=19
d=0.5

hence we know a and d we can find Ap
that is
a,a+0.5,a+2(0.5),a+3(0.5),a+4(0.5).....
as we know ap form
hence AP is

1,1.5,2,2.5,3.......20.
here is your answer
hope it's help you