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AMC 10 USA Math Olympiad

Math Game – Australian Mathematics Competition, 2014

The simplest example of power mean inequality is the arithmetic mean – geometric mean inequality. Learn in this self-learning module for math olympiad

Problem – Math Game (AMC UP – 15)


Sally thinks of a number, multiplies it by 2, adds 2, divides by 2 and then subtracts 2. Her answer is 2. What was her original number?

  • 1
  • 2
  • 3
  • 5

Key Concepts


Math Game

Arithmetic

Missing Number

Check the Answer


Answer: 3

Australian Mathematics Competition Upper Primary

2014 UP 15

Secrets of Mental Math – Arthur T. Benjamin

Try with Hints


This sum is a tricky one. You can play game with this sum too

First we can start with a diagram where the number by which we are starting is X (assume).

In Hint 1 its clear that how to solve this problem.Try this ….

But if you really want a final hint then we have to solve it in reverse.Lets See another picture.

So the answer is 3.

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