Holey Cards are five very inexpensive, timed-drill tools for working on basic math facts in addition, subtraction, multiplication (at two levels of difficulty), and division. The cards (one for each math function except for two for multiplication) have math facts arranged in rows with holes where answers should be. The cards fold in half. We insert a piece of paper in the middle and students write answers in the holes, completing as many problems as they can within the time limit. Because problems are arranged in random order, and there are 100 problems on each card, students cannot easily memorize the placement of answers.
Cards with answers serve as answer keys, so you probably want to invest in the keys to save time. Notice that all five cards and keys would still cost less than $5!