Puzzle

Mr Golan asked the class to see if they could find the sum of the first 50 odd numbers. As everyone settled down to their addition, Julia ran to him and said, "The sum is 2,500." Mr Golan thought, "Lucky guess," and gave him the task of finding the sum of the first 75 odd numbers. Within 20 seconds, Julia was back with the correct answer of 5,625.
How did she do this?

Actually all you have to do is square the number of odd numbers you want added ie

The sum of the first 50 odd numbers is 50^2 (50 squared)

The sum of the first 75 odd numbers is 75^2 (75 squared)