In a square, one pair of opposite sides was made 50% longer and the other pair of opposite sides was made 50% shorter. What percent of the square’s area is the area of the new rectangle?

you have a square with an area of 100 meters^2.
if you decrees a pair of opposite sides by 50%. you end up with a rectangle with the area of 50 meters^2.
then you increase the other pair of opposite sides by 50%. you end up with a rectangle with the area of 75 meters^2. OK now I see what I did wrong. 

The correct answer is 75%