From 1veritasium, 2veritasium, or sciencium.

Observations over millenia and numerous experiments claim that warmer water freezes faster than cold water under identical conditions.
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References:
Mpemba Effect: https://en.wikipedia.org/wiki/Mpemba_effect

Questioning the Mpemba Effect: http://www.nature.com/articles/srep37665

Royal Society of Chemistry competition: http://www.rsc.org/learn-chemistry/resource/res00001018/the-mpemba-effect?cmpid=CMP00007615

Edited by Trevor Carlee