Question

2+4+6+............+40 is ?

Answer 1

Tn = a + (n - 1 )d

40 = 2 + ( n - 1 )× 2

38 / 2 = n - 1

19 +1 = n

n = 20

Sn = n / 2 ( a + l )

10 ( 2 + 40 )

= 420 Ans.