Calculate the sum of first 39 natural numbers.
Answers.
A) 780 B) 891 C) 812 D) 847 E) 890

Rationale: "solution we know that ( 1 + 2 + 3 + . . . . . + 39 ) = n ( n + 1 ) / 2 therefore ( 1 + 2 + 3 + . . . . + 39 ) = ( 39 × 40 / 2 ) = 780 . answer a"
Answer: A