A sum is the total that results when a group of lotto numbers are added together. For example, if a drawing result is 1-12-28-31-45, the sum is 1+12+28+31+45=117. Most sums of winning number combinations fall within a relatively small range of sums, since it is usually the case that there is a mix of low and high numbers drawn and not numbers with an extremely low or high total sum. The Most Probable Range of Sums is useful when selecting your lotto numbers since it is a guide for which sums to stay between.