Addition
In this topic you will
- Add a three-digit number and a one-digit number by regrouping the ones.
- Estimate and add a three-digit number and a two-digit number by regrouping the ones.
- Estimate and add two three-digit numbers by regrouping the ones.
Key Words
- compose
- decompose
- exchange
- regroup
- single
Show Definitions
- compose: To put numbers together to make a larger number.
- decompose: To break a number into smaller parts, such as hundreds, tens, and ones.
- exchange: To trade a group of ones for a ten, or a group of tens for a hundred when calculating.
- regroup: To rearrange numbers by exchanging ones, tens, or hundreds to help with addition or subtraction.
- single: A number that has only one digit.
Building on What You Know
Y ou can already add two two-digit numbers. In this unit, you will learn how to add numbers with up to three digits. You will also learn what to do when there are too many ones in the ones place.
💡 Quick Math Tip
Too many ones: When the ones add up to more than nine, regroup by exchanging ten ones for one ten before continuing the addition.
❓ EXERCISES
$1.$ Choose a number from each number jar to add together. Show your method. Do this three times.
👀 Show answer
$2.$ Read across the grid or down the grid to find a $3$-digit number. Then choose a single digit from any square in the grid to add to your number. Show your method. Do this three times.
👀 Show answer
🧠 Reasoning Tip
Round each number to the nearest $10$ to help you estimate your answer.
$3.$ On Tuesday, $134$ adults and $53$ children visited the library. How many people visited the library on Tuesday? Estimate and then find the total. Show your method.
👀 Show answer
$4.$ On Thursday, $215$ adults and $67$ children visited the museum. How many people visited the museum on Thursday? Estimate and then find the total. Show your method.
👀 Show answer
$5.$ A baker made $148$ chocolate cakes and $136$ lemon cakes. Estimate and then calculate how many cakes the baker made. Show your method.
👀 Show answer
$6.$ The school library has $439$ fiction books and $326$ non-fiction books. Estimate and then calculate how many books the library has all together. Show your method.
👀 Show answer
🧠 Think like a Mathematician
Kiko spilt some ink on the ones digits in her calculation.
$24\Box + 13\Box = 381$
What could her calculation have been?
Did you find all the possibilities for Kiko’s calculation?
Compare your solutions with those of other learners in your class.
👀 Show Answers
- The hundreds and tens digits are fixed, so the missing ones digits must add to $11$.
- Possible pairs for the ones digits include: $2 + 9$, $3 + 8$, $4 + 7$, $5 + 6$.
- Example calculations include: $242 + 139 = 381$ and $245 + 136 = 381$.
- There are multiple correct answers, as long as the ones digits add to $11$.