Number Trick Riddle

John asked the class to see if they could find the sum of the first 50 odd numbers. As everyone settled down to their addition, David ran to her and said, 'The sum is 2,500.' Ms. John  thought, 'Lucky guess,' and gave him the task of finding the sum of the first 75 odd numbers. Within 20 seconds, David was back with the correct answer

How does David find the sum so quickly and what is the answer of this trick question ??

For Answer

First use your mind, then click to see the answer

The following pattern holds: The sum is equal to n x n, when n is the number of consecutive odd numbers, starting with 1. For example, the sum of the first 3 odd numbers is equal to 3 x 3, or 9; the sum of the first 4 odd numbers is equal to 4 x 4, or 16; the sum of the first 5 odd numbers is equal to 5 x 5, or 25; and so on.