1. ## Icosahedron

A special die is made in the shape of an icosahedron, and its faces are numbered with the numbers 1 to 20.
When the die is thrown there is an equal chance of any face landing uppermost. If the die is thrown once, what is the probability that the face that lands uppermost has a number that is a factor of 20?

Solution:

Factors of 20: 1, 2, 4, 5, 10, 20

Let A = probability that the face that lands uppermost has a number that is a factor of 20.

P(A) = 6/20 = 3/10

Is this right?

Yes, it is.

3. ## Re: Icosahedron

Originally Posted by harpazo
A special die is made in the shape of an icosahedron, and its faces are numbered with the numbers 1 to 20.
When the die is thrown there is an equal chance of any face landing uppermost. If the die is thrown once,
what is the probability that the face that lands uppermost has a number that is a factor of 20?
Why do problem setters not keep it simple; like:

A deck of 20 cards, cards labelled 1 to 20.
Deck shuffled, a card then picked at random.
What is the probability that a number that is a factor of 20 is picked?

4. ## Re: Icosahedron

Originally Posted by HallsofIvy
Yes, it is.
Ok. Another one for my notes.