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A dice is rolled three times and sum of three numbers appearing on the uppermost face is 15. The chance that the first roll was a 4 is ?
None of these
03-Oct
01-Jun
01-May
02-May
None of these
03-Oct
01-Jun
01-May
02-May
Solution
The number of possibilities to get sum of three numbers appearing on the uppermost face 15 is:
(4, 5, 6), (4, 6, 5), (6, 4. 5), (6, 5, 4), (5, 6, 4), (5, 4, 6),(5, 5, 5), (3, 6, 6), (6, 3, 6) and (6, 6, 3)
Total possibilities = 10
Number of cases in which first roll was a 4 is = (4, 5, 6) and (4, 6, 5)
Favourable possibilities = 2
Required probability = 2/10 = 1/5
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