20june2019 paper1 Q18
0. The sum of all even natural numbers between 1 and 81 is:
- Option : D
- Explanation : Even number between 1 to 81 are 2, 4, 6, 8,
...... 78,80.
Number of even number between 1 to 81
81-1/2 = 80/2 = 40
Sum of all even numbers = n/2[a+b] where,
n = number of numbers = 40
a = first number = 2
b = last number = 80
Sum = 40/2[2+80]
= 20 x 82 = 1640
