Find the sum of all even numbers less than or equal to 280 (i.e., below 281).

Introduction / Context:
Even integers up to 280 form an AP with d = 2. Summation follows the standard AP method.

Given Data / Assumptions:

• First term = 2, last term = 280, d = 2.
• “Below 281” implies including 280.

Concept / Approach:
Compute term count n = last/2, then apply S_n = n/2 * (first + last).

Step-by-Step Solution:
n = 280/2 = 140.S = 140/2 * (2 + 280) = 70 * 282 = 19,740.

Verification / Alternative check:
S = n * average = 140 * (2 + 280)/2 = 140 * 141 = 19,740.

Why Other Options Are Wrong:
19730/19750/19760 are off by one step in averaging or by arithmetic slip.

Common Pitfalls:
Using 139 or 141 terms mistakenly; forgetting that 280 is even and should be included.

Final Answer:
19740