Subtraction As An Unknown-Addend Problem - 1st Grade Math

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

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

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

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

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

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

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

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

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

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

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

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

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

   $0$. Any number minus itself equals zero.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    $0$. Any number plus zero equals itself.

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

    $0$. Any number minus itself equals zero.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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