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Word problemsArithmeticMiddle schoolabout 0:45

The average of 70, 80, 90 and x is 85. Find x: animated lesson

A narrated, step-by-step word problems video lesson with captions. Final answer: x = 100.

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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
The average of 70, 80, 90 and x is 85. Find x.
2. Step by step
1. Total needed
2. Solve for x
3. The answer
$\text{x = 100}$
x = 100
4. Check
- (70 + 80 + 90 + 100) / 4 = 85 ✓

Transcript

The problem. Here is the problem: The average of 70, 80, 90 and x is 85. Find x. The mean of 70, 80, 90 and x is 85.

Step by step. Total needed. 4 values with mean 85 sum to 4 times 85 equals 340. Solve for x. x equals 340 minus (70 plus 80 plus 90) equals 340 minus 240 equals 100.

The answer. So the answer is x equals 100. The mean of 70, 80, 90 and x is 85.

Check. (70 plus 80 plus 90 plus 100) / 4 equals 85, which checks out.

About word problems

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

The average of 70, 80, 90 and x is 85. Find x (Lesson)