Q21 of 98 Page 686

When two dice are tossed together, find the probability that the sum of numbers on their tops is less than 7.

Total numbers of elementary events are: 6x6 = 36

Let E be the event of getting the sum of numbers on top is less than 7


The favourable combinations are: (1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (2, 1), (2, 3), (2, 2),


(2, 4), (3, 1), (3, 2), (3, 3), (4, 1), (4, 2), (5, 1)


Then, the number of favourable events = 15


∴ P (sum of numbers on top is less than 7) = P (E) = 15/36 = 5/12


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