Choosing balls

Task number: 3535

A bag contains 10 glass balls and 20 clay balls. We choose 7 balls at random. What is the probability that exactly 3 glass balls will be chosen if:

  • Variant

    We do not return balls to the bag.

  • Variant

    We choose balls one by one and return each one to the bag immediately.

Difficulty level: Easy task (using definitions and simple reasoning)
Reasoning task
Routine calculation training
Cs translation
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