Finger Theory Method
Finger theory is all about counting and calculating with our fingers. Since we are limited to 10 fingers, we can only work with single and double-digit numbers. Simply put, we use our right hand for numbers in the ones place and our left for numbers in the tens place. We always count, or add, left to right with the right hand, starting with the index finger. Conversely, we count, or add, right to left with the left hand. When subtracting, we do the reverse. The figure below illustrates how we use fingers to represent single and double-digit numbers.