Doubling numbers is a really common mathematical process, for all sorts of purposes.
Students should be encouraged to learn to double numbers beyond the basic number facts in their heads, when the numbers allow it.
You know, I have realized (a bit late in life, perhaps) an interesting fact about doing mental math.
If someone has good recall of all the basic number facts, there are lots of math questions which we would traditionally have handled with a written algorithm, which could be completed in one’s head.
In fact, I can’t think of a 2-digit addition question that you couldn’t complete mentally.
These questions are like that: can you double a 2-digit number, in your head? Answer: Yes, if I can remember my doubles basic facts, and I know place value.
For example, double 38:
The worksheets go on to 3-digit examples, which should still be within the capabilities of anyone who has memorized number facts.
These questions are already advanced, compared to basic number facts. But you can extend them further: just make the numbers bigger, or try it with decimal fractions, perhaps. For example: