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The Mean Problem

Age 11 to 14
ShortChallenge Level Yellow starYellow star
Secondary curriculum
  • Problem
  • Solutions


four unknown numbers


There are four unknown numbers.

The mean of the first two numbers is 4.

The mean of the first three numbers is 9.

The mean of all four numbers is 15.

If one of the four numbers is 2, what are the others?


You can find more short problems, arranged by curriculum topic, in our short problems collection.

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The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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