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Dolly Dolphin

Age 14 to 16
ShortChallenge Level Yellow starYellow star
Secondary curriculum
  • Problem
  • Solutions

Dolly Dolphin swims at a constant speed. When she swims against a current of 2m/s, she travels at 6 m/s.

Dolly swims upstream in this current for 2 minutes, then turns round and swims back to her starting point. What is her average speed?



This problem is adapted from the World Mathematics Championships
You can find more short problems, arranged by curriculum topic, in our short problems collection.

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One night two candles were lit. Can you work out how long each candle was originally?

Percentage Unchanged

If the base of a rectangle is increased by 10% and the area is unchanged, by what percentage is the width decreased by ?

Digit Sum

What is the sum of all the digits in all the integers from one to one million?

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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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