1/4 of 2 1/2 is equal to 1/4 * 2 1/2 which equals 5/8. She gave 5/8 pounds of blueberries to her students on Monday.
2 1/2 - 5/8 = 1 7/8, so she had 1 7/8 pounds of blueberries left.
1/3 of 1 7/8 is 5/8 so she ate 5/8 pound of blueberries out of the 1 7/8 left.
Mrs. O gave the same amount of blueberries on Monday and ate the same amount of blueberries on Tuesday. (5/8 = 5/8)