1st Grade Math Flashcards: Subtraction As An Unknown Addend Problem

What this deck covers

This deck focuses on Subtraction As An Unknown Addend Problem, giving you a quick way to review the definitions, rules, and examples that matter most for 1st Grade Math.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is the missing number $x$ in $5+x=9$ (so $9-5=x$)?

Answer: $4$. Find what number added to $5$ makes $9$.

Flashcard 2: What is the missing number $x$ in $3+x=15$ (so $15-3=x$)?

Answer: $12$. Find what number added to $3$ makes $15$.

Flashcard 3: What is the missing number $x$ in $4+x=11$ (so $11-4=x$)?

Answer: $7$. Find what number added to $4$ makes $11$.

Flashcard 4: What is the missing number $x$ in $10+x=14$ (so $14-10=x$)?

Answer: $4$. Find what number added to $10$ makes $14$.

Flashcard 5: What is the unknown addend in the equation $4+?=4$?

Answer: $0$. Since $4+0=4$, the missing addend is $0$.

Flashcard 6: What is $6-2$ using the unknown-addend equation $2+?=6$?

Answer: $4$. Find what adds to $2$ to make $6$: $2+4=6$.

Flashcard 7: What is the missing number $x$ in $11+x=11$ (so $11-11=x$)?

Answer: $0$. Any number minus itself equals zero.

Flashcard 8: What is the missing number $x$ in $8+x=10$ (so $10-8=x$)?

Answer: $2$. Find what number added to $8$ makes $10$.

Flashcard 9: What is the unknown addend in the equation $5+?=7$?

Answer: $2$. Since $5+2=7$, the missing addend is $2$.

Flashcard 10: What is $8-3$ using the unknown-addend equation $3+?=8$?

Answer: $5$. Find what adds to $3$ to make $8$: $3+5=8$.

Flashcard 11: What is $7-5$ using the unknown-addend equation $5+?=7$?

Answer: $2$. Find what adds to $5$ to make $7$: $5+2=7$.

Flashcard 12: What is $4-4$ using the unknown-addend equation $4+?=4$?

Answer: $0$. Find what adds to $4$ to make $4$: $4+0=4$.

Flashcard 13: What is $10-8$ by finding the number that makes $10$ when added to $8$?

Answer: $2$. Find what adds to $8$ to make $10$: $8+2=10$.

Flashcard 14: What is the unknown addend in the equation $8+?=10$?

Answer: $2$. Since $8+2=10$, the missing addend is $2$.

Flashcard 15: What is the unknown addend in the equation $3+?=8$?

Answer: $5$. Since $3+5=8$, the missing addend is $5$.

Flashcard 16: What is the missing number $x$ in $13+x=20$ (so $20-13=x$)?

Answer: $7$. Find what number added to $13$ makes $20$.

Flashcard 17: What is the missing number $x$ in $1+x=10$ (so $10-1=x$)?

Answer: $9$. Find what number added to $1$ makes $10$.

Flashcard 18: What is the missing number $x$ in $14+x=18$ (so $18-14=x$)?

Answer: $4$. Find what number added to $14$ makes $18$.

Flashcard 19: What is the missing number $x$ in $2+x=9$ (so $9-2=x$)?

Answer: $7$. Find what number added to $2$ makes $9$.

Flashcard 20: What is the unknown addend in the equation $0+?=4$?

Answer: $4$. Since $0+4=4$, the missing addend is $4$.

Flashcard 21: What is $4-0$ using the unknown-addend equation $0+?=4$?

Answer: $4$. Find what adds to $0$ to make $4$: $0+4=4$.

Flashcard 22: What is $10-7$ by solving the unknown-addend equation $7+?=10$?

Answer: $3$. Find what adds to $7$ to make $10$: $7+3=10$.

Flashcard 23: What is the missing number $x$ in $12+x=16$ (so $16-12=x$)?

Answer: $4$. Find what number added to $12$ makes $16$.

Flashcard 24: Which subtraction matches the unknown-addend equation $6+x=10$?

Answer: $10-6=x$. The subtraction that finds what added to $6$ gives $10$.

Flashcard 25: What is the missing number $x$ in $8+x=16$ (so $16-8=x$)?

Answer: $8$. Find what number added to $8$ makes $16$.

Flashcard 26: What is the missing number $x$ in $0+x=6$ (so $6-0=x$)?

Answer: $6$. Zero plus any number equals that number.

Flashcard 27: What is the unknown addend in the equation $2+?=6$?

Answer: $4$. Since $2+4=6$, the missing addend is $4$.

Flashcard 28: What is the missing number $x$ in $7+x=7$ (so $7-7=x$)?

Answer: $0$. Any number plus zero equals itself.

Flashcard 29: What is the missing number $x$ in $9+x=9$ (so $9-9=x$)?

Answer: $0$. Any number minus itself equals zero.

Flashcard 30: What is the missing number $x$ in $17+x=19$ (so $19-17=x$)?

Answer: $2$. Find what number added to $17$ makes $19$.

Flashcard 31: What does $a-b=c$ mean as an unknown-addend addition sentence?

Answer: $b+c=a$. Subtraction reverses to addition by switching the difference and subtrahend.

Flashcard 32: What is $10-9$ by finding the number that makes $10$ when added to $9$?

Answer: $1$. Find what adds to $9$ to make $10$: $9+1=10$.

Flashcard 33: What does $a-b=?$ mean as an unknown-addend problem written with addition?

Answer: Find $?$ so that $b+?=a$. Subtraction finds what number added to $b$ gives $a$.

Flashcard 34: What is the unknown addend in the equation $7+?=10$?

Answer: $3$. Since $7+3=10$, the missing addend is $3$.

Flashcard 35: What is the unknown addend in the equation $9+?=10$?

Answer: $1$. Since $9+1=10$, the missing addend is $1$.

Flashcard 36: What does $a-b$ mean when you rewrite it as an unknown-addend equation?

Answer: $b+x=a$. Subtraction $a-b$ asks what number added to $b$ gives $a$.

Flashcard 37: What is the missing number $x$ in $9+x=12$ (so $12-9=x$)?

Answer: $3$. Find what number added to $9$ makes $12$.

Flashcard 38: What is $9-6$ by solving the unknown-addend equation $6+?=9$?

Answer: $3$. Since $6+3=9$, the answer is $3$.

Flashcard 39: What is the related addition sentence for $9-6$ using an unknown addend?

Answer: $6+?=9$. Rewrite subtraction as finding what adds to $6$ to get $9$.

Flashcard 40: What is the missing number $x$ in $6+x=13$ (so $13-6=x$)?

Answer: $7$. Find what number added to $6$ makes $13$.