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Averages · Question 10 of 62

Question 10

MediumOriginal question

The average of four numbers is 30. The average of the first three of them is 26. What is the fourth number?

Options for question 10

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. Total of four = 4×30=1204 \times 30 = 120.

  2. Total of first three = 3×26=783 \times 26 = 78.

  3. Fourth = 120−78=42120 - 78 = 42.

Worth noting

Shortcut: the fourth must make up the shortfall of 4 on each of the other three: 30+3×4=4230 + 3 \times 4 = 42. Using 4×44 \times 4 gives 46.

Concept
Missing value when a subgroup average is known
Typical time
50 s
Your time
—
The rule this testsSimple average
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Ten questions from Averages, at your own pace.

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