Basic Mathematics

Finding the Missing Numbers in Equations

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Finding the Missing Numbers in Equations

Sometimes equations leave out a number in the sentence and ask you to find the missing number.

In this lesson, you must find a missing number. In each equation, the missing number is shown as a box (□). Sometimes other symbols are used to replace the numbers, such as ?, x, y, a, b, etc.

What numbers belong in the boxes to make the number sentences true?

8 + 13 = □ Answer: 8 + 13 = 21
7 − □ = 3 Answer: 7 − 4 = 3

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

6 + 24 = □

Question 1 of 8

6 + 24 is not equal to 32. Try again.

6 + 24 is not equal to 28. Try again.

6 + 24 = 30 is a true sentence.

6 + 24 is not equal to 20. Try again.

One of these numbers makes a true sentence. Try again.

6 + 24 equals what number?

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

9 × □ = 63

Question 2 of 8

9 × 9 = 81, not 63. Try again.

9 × 8 = 72, not 63. Try again.

9 × 7 = 63 is a true sentence.

9 × 6 = 54, not 63. Try again.

One of these numbers makes a true sentence. Try again.

9 times what number is equal to 63?

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

84 ÷ □ = 6

Question 3 of 8

84 × 18 = 4 R12, not 6. Try again.

84 × 21 = 4, not 6. Try again.

84 × 16 = 5 R4, not 6. Try again.

84 × 14 = 6 is a true sentence.

One of these numbers makes a true sentence. Try again.

84 divided by what number is equal to 6?

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

9 + □ = 23 − 6

Question 4 of 8

9 + 9 = 18, but 23 − 6 = 17. Try again.

9 + 8 = 23 − 6 is a true sentence because both sides equal 17.

9 + 6 = 15, but 23 − 6 = 17. Try again.

9 + 7 = 16, but 23 − 6 = 17. Try again.

One of these numbers makes a true sentence. Try again.

First, simplify the expression on the right: 23 − 6 = 17

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

30 ÷ □ = 18 ÷ 3

Question 5 of 8

30 ÷ 3 = 10, but 18 ÷ 3 = 6. Try again.

30 ÷ 5 = 18 ÷ 3 is a true sentence because both sides equal 6.

30 ÷ 6 = 5, but 18 ÷ 3 = 6. Try again.

30 ÷ 15 = 2, but 18 ÷ 3 = 6. Try again.

One of these numbers makes a true sentence. Try again.

First, simplify the expression on the right: 18 ÷ 3 = 6

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

4 × 5 = 18 + □

Question 6 of 8

4 × 5 = 18 + 2 is a true sentence because both sides equal 20.

4 × 5 = 20, but 18 + 7 = 25. Try again.

4 × 5 = 20, but 18 + 20 = 38. Try again.

4 × 5 = 20, but 18 + 6 = 24. Try again.

One of these numbers makes a true sentence. Try again.

First, simplify the expression on the left: 4 × 5 = 20

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

(8 × □) + (10 × □) = 16 + 20

Question 7 of 8

(8 × 6) + (10 × 6) = 48 + 60, not 16 + 20. Try again.

(8 × 2) + (10 × 2) = 16 + 20 is a true sentence because both sides equal 36.

(8 × 3) + (10 × 3) = 24 + 30, not 16 + 20. Try again.

(8 × 1) + (10 × 1) = 8 + 10, not 16 + 20. Try again.

One of these numbers makes a true sentence. Try again.

First, simplify the expression on the right: 16 + 20 = 36

Finding the Missing Numbers in Equations

Click on the number that belongs in the box.

5 × (8 + □) = 55

Question 8 of 8

5 × (8 + 5) = 5 × 13 or 65, not 55. Try again.

5 × (8 + 3) = 55 is a true sentence because 5 × 11 = 55.

5 × (8 + 11) = 5 × 19 or 95, not 55. Try again.

5 × (8 + 1) = 5 × 9 or 45, not 55. Try again.

One of these numbers makes a true sentence. Try again.

5 times what number is equal to 55?

Finding the Missing Numbers in Equations