A fourth of the initial number of bees is 80000 bees / 4 = <<80000/4=20000>>20000 bees
The number of bees that has to die is 80000 bees – 20000 bees = <<80000-20000=60000>>60000 bees
For the colony to reach a fourth of its population, 60000 bees ÷ 1200 bees/day = <<60000/1200=50>>50 days have to pass.
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