[MA2019] (1) 13 :
13. Add within 100, using concrete models or drawings and strategies based on place value.
a. Add a two-digit number and a one-digit number.
b. Add a two-digit number and a multiple of 10.
c. Demonstrate that in adding two-digit numbers, tens are added to tens, ones are added to ones, and sometimes it is necessary to compose a ten.
d. Relate the strategy for adding a two-digit number and a one-digit number to a written method and explain the reasoning used.