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Speedy Sidney

Age 11 to 14
Challenge Level Yellow starYellow starYellow star
  • Problem
  • Student Solutions

The problem can be solved by considering the relative speed of the trains.

The speed of approach of the trains is 125 km/h on a 100 km track, so they will collide after a time 100/125 = 4/5 hour. Sidney flies at 100 km/h for 4/5 hour so he flies 80 km.

Finally, if Sidney were to fly exactly 100 km, the relative speed of the trains would be 100 km/h, provided Sidney was continuing to fly at 100 km/h. OR ..... there is another way - do you have any suggestions?

We received the correct solutions from: Stephen Smith(South Greenhoe Middle School).


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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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