Find the Unknown in Addition and Subtraction Equations

Students will determine the missing whole number that makes an addition or subtraction equation true. The unknown can appear in any position — as a missing addend, minuend, or subtrahend — in equations within 20.

Try three of them

Real questions from this skill, graded here. No account, and nothing is saved.

Grade 1 · Equations and the Equal Sign · question 1 of 3

0 of 12

12 rungs. A star at the top.

7 − = 4.

How it is taught

0:00 of 3:04

An unknown is a missing number.

A missing addend completes the sum.

Read it: Find the missing part: count on

8 + ? = 13. Start at 8 and count on to 13: 9, 10, 11, 12, 13. That is 5, so 8 + 5 = 13.

Start at the part you know: 8.
Count on to the whole: 9, 10, 11, 12, 13.
The number you counted on is the missing part: 5.

The whole is the 2 parts together, so one part and the missing part make 13.

Counting on from 8 counts only the missing part.

A take-away hides the same thing: 13 − 8 is the 5 that makes 8 into 13.

Start at the part you know. Count on to the whole. The count on is the missing part.

Adding the 2 numbers you see: 8 + 13 = 21.

13 is the whole already. Count on from 8 to 13: 5.

9 + ___ = 12 — 3. Count on from 9 to 12: 10, 11, 12. That is 3.

8 + ? = 14

Sam had eight stickers. His friend gave him some more. Now Sam has fourteen stickers. How many did his friend give him?

We can write this as eight plus something equals fourteen. The question mark is the number we need to find.

Let's use a number line to help us. We start at eight.

We need to land on fourteen. How many jumps will it take?

Count up: nine, ten, eleven, twelve, thirteen, fourteen — that's six jumps!

So the missing number is six. We write six in the box.

Let's check our work: eight plus six equals fourteen. It works!

The unknown is six. When one part is missing, we can count up to find it. Great work!

Grade 1 · Counting up to find the missing number

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

More of the library

Every skill has a page

Practise this skill free

14 days of every skill, practice packets, Fluency sheets and up to four students. No card.

Start free