Question

Break apart the addends to find the sum 18+21

Answer 1

We break apart the first numer:

10+8

the second:

20+1

and add like this:

18+21=10+8    +  20+1

now, we can mix up the order:

18+21=10+8    +  20+1= 10+20     + 8+1

add the parts:

18+21=10+8    +  20+1= 10+20     + 8+1=30+9=39