Division by zero and why it doesn't work
A simple explanation on why we cannot divide by zero. We prove why 7 divided by zero, for example, does not work by looking at the corresponding multiplication. If 7 ÷ 0 was, say, 0, then the corresponding multiplication would say 0 × 0 = 7, which is clearly wrong.
Some people suggest that zero divided by zero should equal zero. But that presents problems, also. We could just as easily say that zero divided by zero equals 4 (or some other number), because the multiplication check would work: 4 × 0 = 0. Zero divided by zero is therefore said to be UNDEFINED.
In a summary, children learning this in 3rd grade can simply remember that you are not allowed to divide by zero -- it just doesn't work.
In the latter part of the lesson I go through some varied practice problems concerning division and we also solve one word problem.
See also
Division word problems versus multiplication word problems
Math Mammoth Grade 3 curriculum