Question

find the sum of all given terms of the A.P 4,8,12......20

Answer 1

4+8+12+16+20=60 
ans:60

Answer 2

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.
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