Cartoon numbers are used to illustrate how you can change one number into a larger number by adding hundreds, tens and units in a simple process. In the first example, 158 is turned into 258 by adding 100. In the second example, 438 is turned into 679 by first adding a single unit to make 439, then adding 40 to make 479, and finally adding 200 to get 679.
Students could be given a number of problems involving the addition of hundreds, tens and units. Different coloured pens could be used to write the hundreds, tens and units respectively and students could add the numbers for each colour separately, then consider the numbers side by side for the final answer.