1365. In some areas, on average, for every 100 watermelons grown, one weighs not less than 10 kg. Find the probability that a batch of watermelons from this area containing 400 pieces will: a) exactly 3 watermelons weighing not less than 10 kg each; b) at least three such watermelons.

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)