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Word problemsArithmeticMiddle schoolabout 0:44

Half of a number is 9. What is the number?: animated lesson

A narrated, step-by-step word problems video lesson with captions. Final answer: The number is 18.

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Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.3 MB) · Captions (WebVTT)

Steps on screen

1. The problem
Worked example
Half of a number is 9. What is the number?
2. Step by step
1. Read the problem
2. Solve the linear equation
3. The answer
$\text{The number is 18}$
The number is 18
4. Check
- Substitute x = 18: (1/2)*(18) = 9 ✓

Transcript

The problem. Here is the problem: Half of a number is 9. What is the number? Let x be the number: “half of a number” becomes (1 over 2) times x.

Step by step. Read the problem. Let x be the unknown number. “half of a number is 9” translates to (1 over 2) times x equals 9. Solve the linear equation. 0.5x plus 0 equals 9 → x equals (9 minus 0) / 0.5 equals 18.

The answer. So the answer is The number is 18. Let x be the number: “half of a number” becomes (1 over 2) times x.

Check. Substitute x equals 18: (1 over 2) times (18) equals 9, which checks out.

About word problems

Turn everyday situations about prices, speed, ages and interest into equations and solve them.

Half of a number is 9. What is the number?: Animated Lesson