Add and subtract two-digit numbers

To add or subtract, split the second number into tens and ones and jump along a number line. Jump the tens first, then the ones. When the ones cross a ten, jump to the ten first and then jump the rest. A number sentence can have a missing part: the whole is the biggest number, so take the known part away from it to find the missing part. For a story with two steps, do one step at a time and write a number sentence for each.