Question

sum of first and fifth term of an ap 18 and 4th term exists twice first term by 2 find the sum of first 20 terms​

Answer 1

first term(a). common difference (d)

here,

According to ques

a + (a+4d) = 18

or,2a + 4d = 18

.•. a+2d = 9

.°. a= 9-2d

and

according to second part

2a*2=4th term

4a=a+3d

36--8d=9-2d+3d

9d=27

d=3

also

a=9-2*3=3

then

sum of first 20terms = (n/2){2a+(n-1)d}=630

if not correct please

and please clear me 2nd part of the question fast...