Break apart the addends. Solve for the total sum.
18
+ 21
--------
10 + 8 + 20 + 1 =
or
20 - 2 + 20 + 1
39
start on the right. 8+1=9 move to the left side. 1+2= 3. the solution to this problem is 39
go to the right.8+1=9
go to the left.1+2=3
it is 39.
10+8+20+1= 39
39
18 + 21 = 39
Answer:
39