A box contains 3 defective lightbulbs and 7 non-defective lightbulbs. Two bulbs are drawn at random without replacement. What is the probability of drawing at least one defective bulb?

Answer and explanation

Correct answer: C.

  1. Step 1: Use the complement rule: . Step 2. Probability of drawing two non-defective bulbs: . Step 3. Subtract from 1: . **Answer: . Why not the others:** is the probability of zero defective bulbs; assumes replacement; is the fraction of defective bulbs in the box.

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A box contains 3… | Riigieksamid (Estonian State Exams)