Answer:
Step-by-step explanation:
23 shelves on the book shelf
You can use a tangent:

We have opposite = 17 and adjacent = x.

substitute:
cross multiply
multiply both sides by √3

divide both sides by 3

Use the Pythagorean theorem:

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Other method.
triangle.
The sides are in the ratio 
Therefore

12/50 is the probability of rolling a 3
12/50= He has a 24% chance of rolling a three