Find the Missing Number
Aligned to 3.OA.A.4 — Common Core State Standards for Mathematics.
What this lesson teaches
Sometimes one number in an equation is hidden. Use facts you know to find the number that makes the equation true.
Worked examples
Example 1
Solve 4 × ? = 24. Ask: 4 times what equals 24? Count by 4s: 4, 8, 12, 16, 20, 24. That is 6 fours. So the missing number is 6, because 4 × 6 = 24.
Example 2
Solve ? × 7 = 35. Count by 7s: 7, 14, 21, 28, 35. That is 5 sevens, so the missing number is 5.
Example 3
Solve 45 ÷ ? = 9. Ask: 45 split into groups of what size gives 9 groups? 45 ÷ 5 = 9, so the missing number is 5.
Practice questions
- Find the missing number: 3 × ? = 15.
- Find the missing number: ? × 5 = 40.
- Find the missing number: 28 ÷ ? = 7.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Encuentra el Número que Falta
A veces un número de la ecuación está escondido. Usa los hechos que ya sabes para encontrar el número que hace verdadera la ecuación.
Ejemplo 1: Resuelve 4 × ? = 24. Pregunta: ¿4 por cuánto es 24? Cuenta de 4 en 4: 4, 8, 12, 16, 20, 24. Son 6 cuatros. El número que falta es 6, porque 4 × 6 = 24.
Ejemplo 2: Resuelve ? × 7 = 35. Cuenta de 7 en 7: 7, 14, 21, 28, 35. Son 5 sietes, así que el número que falta es 5.
Ejemplo 3: Resuelve 45 ÷ ? = 9. Pregunta: ¿45 dividido en grupos de qué tamaño da 9 grupos? 45 ÷ 5 = 9, así que el número que falta es 5.
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