Calculate the sum of first 28 natural numbers.  Choices:
A) 426
B) 406
C) 401
D) 409
E) 405

Rationale: "solution we know that ( 1 + 2 + 3 + . . . . . + 28 ) = n ( n + 1 ) / 2 therefore ( 1 + 2 + 3 + . . . . + 28 ) = ( 28 × 29 / 2 ) = 406 . answer b"
Answer: B