SHS DirectorySHS MatchLesson PlansGES Promotion Past QuestionsStudent Lesson NotesBlogs

Basic 2 · Mathematics · Number Operations

Adding and Subtracting to 100

In this topic you will add and subtract numbers up to 100 using tens and ones.

By the end of these notes you should be able to:

  • Add two-digit numbers using tens and ones
  • Subtract two-digit numbers using tens and ones
  • Solve story problems up to 100

What you already know

  • Adding and subtracting within 20 (Basic 1)

Copy everything that has a blue line on its left into your notebook. The other parts are for reading.

Strand
Number
Sub-strand
Number Operations
Indicator
B2.1.2.1.1 – Use conceptual understanding of addition and subtraction to add and subtract numbers to, 100

Introduction

Esi sold 34 oranges in the morning and 25 in the afternoon. How many did she sell in all? Let us add tens and ones.

1. Adding Tens and Ones

Example

34 + 25 = ?

  1. Add the ones: 4 + 5 = 9
  2. Add the tens: 30 + 20 = 50
  3. Put them together: 50 + 9 = 59

Answer: 34 + 25 = 59

Bundles of ten and single sticks showing 34 + 25
Figure 1: Adding 34 and 25 with sticks Show 23 + 14 with drawings of bundles and sticks.Illustration: Sirbus

2. Subtracting Tens and Ones

Example

68 – 23 = ?

  1. Subtract the ones: 8 – 3 = 5
  2. Subtract the tens: 60 – 20 = 40
  3. Put them together: 40 + 5 = 45

Answer: 68 – 23 = 45

Column method
TensOnes
68
–23
=45

Tip: Always start with the ones.

New words

add
To put together.
subtract
To take away.
sum
The answer to an addition.
difference
The answer to a subtraction.

Summary

  • Add ones first, then tens.
  • Subtract ones first, then tens.
  • 34 + 25 = 59 and 68 – 23 = 45.

Class activity: Bundle Sums

  1. Make two numbers with bundles and sticks.
  2. Join them and count the tens and ones.
  3. Write the addition sentence.
  4. Take some away and write the subtraction sentence.

You need: Raffia string, Measuring sticks, Assorted empty cups, Bottles, Bottle tops, Number cards

Exercises

Answer in your exercise book first, then check your answers.

  1. 1. 21 + 13 = ?

    • A. 33
    • B. 34
    • C. 35
    • D. 44
    Show answer
    Answer: 341 + 3 = 4 ones; 20 + 10 = 30.

  2. 2. 57 – 32 = ?

    • A. 25
    • B. 24
    • C. 35
    • D. 89
    Show answer
    Answer: 257 – 2 = 5; 50 – 30 = 20.

  3. 3. 40 + 30 = 70

    • A. True
    • B. False
    Show answer
    Answer: True4 tens + 3 tens = 7 tens.

  4. 4. 86 – 41 = 55

    • A. True
    • B. False
    Show answer
    Answer: False86 – 41 = 45.

  5. 5. 52 + 16 = ______

    Show answer
    Answer: 682 + 6 = 8; 50 + 10 = 60.

  6. 6. Kofi had 75 marbles. He gave away 24. How many are left?

    Show answer
    Answer: 51 marbles75 – 24 = 51.

Homework

  1. Make up one adding story and one subtracting story with numbers up to 100. Solve them.