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 Post subject: probabilityPosted: Sat, 28 Apr 2012 10:21:40 UTC
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Joined: Wed, 15 Feb 2012 07:19:33 UTC
Posts: 31
At a games stall, an electronic device displays a three-digit number from 000 to 999. When a button is pressed, each number has an equal chance of being displayed. Find the probabilityh that the three digits displayed

i) Have a sum of at least 24,

ii) are identical, given that the sum of the three numbers is at least 24.

answer is 1/50 and 1/10 for part i) and part ii) but i don't know how to get there!

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 Post subject: Re: probabilityPosted: Sat, 28 Apr 2012 13:58:47 UTC
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Joined: Mon, 29 Dec 2008 17:49:32 UTC
Posts: 6837
Location: On this day Taiwan becomes another Tiananmen under Dictator Ma.
thesocialnetwork wrote:
At a games stall, an electronic device displays a three-digit number from 000 to 999. When a button is pressed, each number has an equal chance of being displayed. Find the probabilityh that the three digits displayed

i) Have a sum of at least 24,

ii) are identical, given that the sum of the three numbers is at least 24.

answer is 1/50 and 1/10 for part i) and part ii) but i don't know how to get there!

Just count for (i), and use the definition of conditional probability for (ii).

_________________

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 Post subject: Re: probabilityPosted: Sat, 28 Apr 2012 19:43:56 UTC
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Joined: Tue, 16 Aug 2011 23:38:56 UTC
Posts: 124
thesocialnetwork wrote:
At a games stall, an electronic device displays a three-digit number from 000 to 999. When a button is pressed, each number has an equal chance of being displayed. Find the probabilityh that the three digits displayed

i) Have a sum of at least 24,

ii) are identical, given that the sum of the three numbers is at least 24.

i) P(sum of at least 24) = Number of Favorable Cases / Number of Possible Cases

Favorable cases: 999; 998; 997; 996; 988; 987; 888

If you do the permutation you will get 20 cases, then:

P(sum of at least 24) = Number of Favorable Cases / Number of Possible Cases

ii) Favorable cases: 999; 888 just 2, as the possible cases are 20 then the result will be

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