On Mary's birthday, her brother surprised her with $100. She spent a quarter of it on a new video game and then used a fifth of what was left on swimming goggles. How much money did she have left?
Think hard. Detailed solution:
60
Mary spent 100 / 4 = 25 dollars on a new video game.

So, after the video game purchase, Mary was left with 100 - 25 = 75 dollars.

Mary then bought swimming goggles for 75 / 5 = 15 dollars.

Mary had 75 - 15 = 60 dollars left.

.

The answer is 60