This document provides instruction on adding two-digit numbers. It explains the formal algorithm for addition by adding the ones and tens places separately, including renaming when the ones place exceeds 9. An example problem of 31 + 20 is worked out step-by-step. It also gives a two-step word problem about Mrs. Tan and Mrs. Lee baking pies that is solved using addition. The goal is to teach students how to add two-digit numbers and solve word problems involving addition.

1. Whole Numbers
Addition Within 100
What will we learn today?
• Adding two 2-digit numbers
• Adding numbers using formal algorithm
• Solving 2-step word problems
involving addition

2. 31 + 20 = _____
Tens Ones
Step 1 : Add the ones.
3 1
1 + 0 = 1
+ 2 0 Step 2 : Add the tens.
3 + 2 = 5
5 1

3. 58 + 9 = _____
Tens Ones Step 1 : Add the ones.
5 8 8 + 9 = 17
1
You cannot have 2 digits on the same
column, so you need to do renaming.
+ 9 17 = 1 ten 7 0nes
You need to add the 1 ten to the tens
place.
6 7
Step 2 : Add the tens.
5 + 1 = 6

4. Word Problem
Mrs Tan baked 26 pies. Mrs Lee baked 5 more pies
than Mrs Tan. How many pies did Mrs Tan and Mrs
Lee bake in all?
1
26 + 5 = 31 2 6 3 1
+ 5 +2 6
31 + 26 = 57 3 1 5 7
They baked 57 pies in all.

5. Are you ready to
try out the
questions?