Question

three unbiased coins are tossed simultaneously.what is probability of getting at most two tails

Answer 1

The outcome of tossing three unbiased coins appears like below. Where H stands for heads and T stands for tails.

Scenario 1: - HHH

Scenario 2: - HHT

Scenario 3: - HTH

Scenario 4: - HTT

Scenario 5: - THH

Scenario 6: - THT

Scenario 7: - TTH

Scenario 8: - TTT

So there are 8 outcomes.

Now the probability of getting at most two tails is nothing but below scenarios

No tail:  - case 1

One tail: - Case 2, 3 and 5

Two tails: - Case 4, 6 and 7

So total 7 chances. Hence the probability is 7/8.