Doubling means: you take the number plus itself.
Example: 15 doubled
15 + 15 = 30, so the double of 15 is 30.
Tip: double the tens first, then the ones.
With 15: 10 + 10 = 20 and 5 + 5 = 10, together 30.
The numbers filled in show the solution.
Example
15+15=30
20+20=40
For parents
What does this exercise practice?
Double numbers confidently and understand the double as the number plus itself.
Common pitfalls
Children often forget the carry with the ones. Saying it out loud helps: 5 plus 5 is 10, that is a new ten.
How to practice at home
Lay out a pile of blocks, then exactly the same amount next to it and count everything together. That makes doubling visible.
Related: Halve, Calculation, Swap