Before kids can work on math problems like addition and subtraction, they must understand number sequence. ‘Gone Missing’ is a free, printable math worksheet that deals with this concept. Children are expected to read each set of numbers and then fill in the blanks with the number that comes in between. This printable math worksheet covers one-digit, two-digit and three-digit numbers. You can also check out the other math topics covered on our 1st grade math worksheets page.