Sample space = HHH, HHT, HTH, THH, TTT, TTH, THT, HTT (8 possibilities)
Desirable outcomes = TTH, THT, TTH (3 possibilities)
Required probability = 3/8
Answer: Approximately 22.62 degrees
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Work Shown:
cos(angle) = adjacent/hypotenuse
cos(y) = 12/13
y = arccos(12/13)
y = 22.6198649
y = 22.62
Notes:
- Arccosine is the same as inverse cosine. On your calculator there should be a button labeled

- Make sure your calculator is in degree mode
- The decimal result for y, shown above, is approximate. I rounded to two decimal places to show the final answer. Round however you need to if your teacher instructs otherwise.