Mathematics
Grade 3
15 min
Fill in the missing digits
Fill in the missing digits
Tutorial Preview
1
Introduction & Learning Objectives
Learning Objectives
Identify the place value of missing digits in an addition problem.
Use basic addition facts to find a missing digit in the ones place.
Solve for a missing digit in the tens place, both with and without regrouping.
By the end of of this lesson, students will be able to determine a missing digit in the hundreds place by applying addition rules.
Apply the concept of regrouping (carrying over) to find missing digits in addends.
Check their answers by performing the complete addition problem.
Ever played detective with numbers? 🕵️ What if a number in your math problem went missing and you had to find the culprit?
In this lesson, you'll become a number detective! We will learn how to find the secret, missing digits in addition problems. We'll use our...
2
Key Concepts & Vocabulary
TermDefinitionExample
DigitA single symbol used to make numbers. The digits are 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.In the number 381, the digits are 3, 8, and 1.
Place ValueThe value of a digit based on its position in a number (ones, tens, hundreds).In the number 529, the 9 is in the ones place, the 2 is in the tens place (worth 20), and the 5 is in the hundreds place (worth 500).
SumThe total or answer you get when you add two or more numbers together.In the problem 7 + 2 = 9, the sum is 9.
AddendAny of the numbers that are added together to get the sum.In the problem 7 + 2 = 9, the numbers 7 and 2 are the addends.
Regrouping (Carrying Over)When the sum of digits in a column is 10 or more, you move the 'tens' part of the sum to the next column on the left.In 29 + 4, the ones col...
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Core Formulas
Finding a Missing Addend
Sum_{column} - Known Addend_{column} = Missing Addend_{column}
To find a missing digit in a column, subtract the digit you know from the digit in the sum for that same column.
The Regrouping Rule
If Sum_{digit} < Known Addend_{digit}, then Sum_{column} = Sum_{digit} + 10
If the digit in the sum is smaller than the addend above it, it means regrouping happened. You must add 10 to the sum's digit before you can subtract to find the missing number.
4 more steps in this tutorial
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Challenging
When solving for a missing digit in an addend, you see that the sum's digit for that column is SMALLER than the addend's digit you know (like _ + 8 = 3). What must you do first before you can subtract?
A.Add 10 to the sum's digit because regrouping must have happened.
B.Guess a number that might work.
C.Subtract the smaller number from the bigger number (8 - 3).
D.Skip that column and come back to it later.
Challenging
Find the missing digit in the tens place for this three-addend problem: 149 + 3_6 + 285 = 810.
A.9
B.8
C.7
D.6
Challenging
Which missing digit for the blank in 5_7 + 286 would require you to regroup in BOTH the tens and the hundreds columns?
A.0
B.1
C.2
D.3
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