Multiple choice

Minimum number of times a fair coin must be tossed so that the probability of getting at least one head is more than 99% is:

  1. 6

  2. 7

  3. 8

  4. 5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Probability of at least one head in n tosses is 1 - (1/2)^n. We want 1 - (1/2)^n > 0.99, so (1/2)^n < 0.01. Since 2^6 = 64 and 2^7 = 128, 1/128 < 0.01. Thus n must be at least 7.

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