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Missing Numbers in Subtraction—Let's Practice!

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Missing Numbers in Subtraction—Let's Practice!
CCSS.MATH.CONTENT.2.OA.A.1, CCSS.MATH.CONTENT.1.OA.A.2

Basics on the topic Missing Numbers in Subtraction—Let's Practice!

Today we are solving missing numbers in subtraction problems with Razzi! This video contains examples to help you further practice and grow confident in this topic.

Transcript Missing Numbers in Subtraction—Let's Practice!

Razzi says get these items ready (...) Because today we're going to practice... Missing Numbers in Subtraction. It's time to begin! Find the missing number in the number sentence... seventy-eight minus blank equals twenty-one. Rewrite the number sentence by moving twenty-one BEFORE the equal sign. Then solve seventy-eight minus twenty-one which equals fifty-seven. Check your answer by putting fifty-seven in the ORIGINAL number sentence. Did you also get seventy-eight minus fifty-seven equals twenty-one? Let's tackle the next problem! Ninety-three minus blank equals ten. Rewrite the number sentence by moving ten BEFORE the equal sign. Then solve ninety-three minus ten which equals eighty-three. Check your answer by putting eighty-three in the ORIGINAL number sentence. Did you also get ninety-three minus eighty-three equals ten? Let's try another! Blank minus twenty-two equals fifty-five. Since the first number is missing in the subtraction sentence, rewrite the number sentence as twenty-two PLUS fifty-five... then solve to get seventy-seven. Check your answer by putting seventy-seven in the ORIGINAL number sentence. Did you also get seventy-seven minus twenty-two equals fifty-five? Let's try one more! Blank minus eighty-nine equals two. Rewrite the number sentence as eighty-nine PLUS two... then solve to get ninety-one. Check your answer by putting ninety-one in the ORIGINAL number sentence. Did you also get ninety-one minus eighty-nine equals two? Razzi had so much fun practicing with you today! See you next time!

Missing Numbers in Subtraction—Let's Practice! exercise

Would you like to apply the knowledge you’ve learned? You can review and practice it with the tasks for the video Missing Numbers in Subtraction—Let's Practice!.
  • Rewrite the problem without missing numbers and solve.

    Hints

    To rewrite the equation, swap 32 with the missing number.

    To find the missing number, solve 45 - 32.

    Solution

    The equation without missing numbers is 45 - 32 = ?.

    Solve 45 - 32 = 13. 13 is the missing number.

    Check your work. Plug 13 back into the original equation 45 - 13 = 32.

  • Solve for the missing number.

    Hints

    Rewrite the equation.

    • Swap the missing number with 16.
    • When the missing number is first in the original equation, change the operation sign to +.

    Solve the new equation

    • What is 16 + 21?
    • Plug the answer into the original equation to check your work.
    Solution

    The missing number is 37.

    • Rewrite the equation as 16 + 21 = ?.
    • Solve the new equation by adding 16 + 21 = 37.
    • Check your work. Plug the missing number, 37, into the original equation. 37 - 21 = 16.
  • Find the missing numbers.

    Hints

    Step 1: Rewrite the equation.

    Swap the missing number with the number to the right of the equal sign.

    So, 46 - ? = 16 should be rewritten as 46 - 16 = ?.

    Step 2: Solve the new equation. What is 46 - 16?

    The image below shows 46 blue dots. 16 are inside a red box.

    Count the number of blue dots outside of the red box to solve the equation.

    Step 3: Check your work.

    When you've found the answer, plug it into the original equation: 46 - ? = 16.

    If you subtract the correct number from 46, you will get 16!

    Solution

    1. 46 - 30 = 16. The missing number is 30.
    • Rewrite the equation as 46 - 16 = ?.
    • Subtract. 46 - 16 = 30.
    2. 59 - 26 = 33. The missing number is 26.
    • Rewrite the equation as 59 - 33 = ?.
    • Subtract. 59 - 33 = 26.
    3. 80 - 11 = 69. The missing number is 11.
    • Rewrite the equation as 80 - 69 = ?.
    • Subtract. 80 - 69 = 11.

  • Find all the missing numbers.

    Hints

    Step one: rewrite the equation

    Rewrite the equation so that the missing number is on the right of the equal sign.

    In this problem, the missing number is first in the original equation. This is shown by the red box in the image below.

    • When the missing number is first, make sure to rewrite your equation with a +.
    • The rewritten equation will be 12 + 45 = ?

    In this problem, the missing number is second.

    • When the missing number is second, do not change the operation sign.
    • Swap the numbers as shown in the image. The new equation will be 78 - 15 = ?
    Solution

    ? - 45 = 12. The missing number is 57.

    • Rewrite the equation as 12 + 45 = ?.
    • Add 12 + 45 = 57.
    • Check your work. Plug 57 into the original equation. Does 57 - 45 = 12? YES!
    ? - 43 = 9. The missing number is 52.
    • Rewrite the equation as 43 + 9 = ?.
    • Add 43 + 9 = 52.
    • Check your work. Plug 52 into the original equation. Does 52 - 43 = 9? YES!
    78 - ? = 15. The missing number is 63.
    • Rewrite the equation as 78 - 15 = ?.
    • Subtract 78 - 15 = 63.
    • Check your work. Plug 63 into the original equation. Does 78 - 63 = 15? YES!

  • What's the missing number?

    Hints

    First, rewrite the equation so that the missing number is on the right of the =. This is done for you in the image.

    Solve the new equation: 51 - 37 = ?

    What is 51 - 37?

    This image shows 51 blue dots. 37 dots are in the red box.

    Count the number of dots outside of the red box to find 51 - 37.

    Solution

    51 - 37 = 14.

    Plug 14 into the original equation to check your work:

    51 - 14 = 37.

  • Solve the word problem.

    Hints

    We can write this problem as a subtraction equation. It is shown below.

    The number of candies Razzi started with (70) - the candies Razzi ate (?) = the number of candies Razzi has left (49).

    Next, rewrite the equation so that the missing number is on the right of the equal sign.

    The rewritten equation is shown below.

    Solve the rewritten equation. The answer tells you how many candies Razzi ate!

    Plug it back into the original equation to check your work.

    Solution

    Razzi ate 21 pieces of candy.

    Step 1: Write the original equation

    • The original equation should be written as 70 - ? = 49.
    Step 2: Rewrite the equation
    • Rewrite the equation as 70 - 49 = ?.
    Step 3: Solve the new equation
    • 70 - 49 = 21.
    Step 4: Check your work
    • Plug 21 into the original equation. Does 70 - 21 = 49? YES!