The Lost Key: A Mystery with Whole Numbers — Melinda Thielbar

At Sifu Faiza's Kung Fu School, kids learn to be strong and fast. They also learn to be smart, cool-headed, and honest. So Joy, Adam, Sam, and Amy are surprised when the key to the school is stolen―as well as all their kung fu gear. Now they'll have to use all kinds of calculations―addition, subtraction, multiplication, and division―to figure out the clues, follow the thieves, and find . . . The Lost Key.