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The-Wrestling-Fanatic
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Doing this past paper and came across this question

A fair die has six faces numbered 1, 2, 2, 3, 3 and 3. The die is rolled twice and the number showing on the uppermost face is recorded each time.

Find the probability that the sum of the two numbers recorded is at least 5.

i got 27/36 but the mark scheme says 21/36.

i cant see where i have made my mistake

can anyone?
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Christophicus
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(Original post by The-Wrestling-Fanatic)
Doing this past paper and came across this question

A fair die has six faces numbered 1, 2, 2, 3, 3 and 3. The die is rolled twice and the number showing on the uppermost face is recorded each time.

Find the probability that the sum of the two numbers recorded is at least 5.

i got 27/36 but the mark scheme says 21/36.

i cant see where i have made my mistake

can anyone?
x: 1 2 3
P(X=x): 1/6 2/6 3/6

P(sum=5) + P(sum=6)
= (2/6)(3/6) + (3/6)(2/6) + (3/6)(3/6)
= 21/36
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The-Wrestling-Fanatic
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Report Thread starter 12 years ago
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thanx mate realised my problem!
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__WiZaRD__
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Draw a sample space. It helps.
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