Question

Sum 2+4+6+8+.......200

Answer 1

we can use ap to solve this question

given that : a = 2

                   d = 2 (4-2, 6-4 , 8-6)

                   an = 200

                   n = ?

              an = a + (n-1)d

   200 = 2 + (n-1)2

    198/2 = n-1

     99 = n-1

    n=100

now , sn = n/2 (a +an)

sn = 100/2 * (2 + 200)

sn = 50 * (202)

sn = 10100 i.e your answer