Question

4+8+12+find the sum of first 20 terms​

Answer 1

common difference (d) = (a2-a1)

                                     = (8-4) = 4

nth term = a+(n-1)d

   20 = 4+4n-4

   20 = 4n

   n = 5

an or last term (l) =  20

first term (a) = 4

sum (s) = n/2 (a+l)

             =  5/2 (4+20)

             = 5/2 (24)

             = 5 x 12 = 60

therefore, answer is 60.