Suppose you roll two dice. How do you find the probability that you'll roll a sum of 7?

1 Answer
Shwetank Mauria
Dec 31, 2016

Probability that you'll roll a sum of #7# is #1/6#

Explanation:

When we roll a dice, we can get numbers #1# to #6# on each of the dices and hence possible combinations are as follows (here #(x,y)# means we get #x# on first dice and #y# on second dice.)

#(1,1)#, #(1,2)#, #(1,3)#, #(1,4)#, #(1,5)#, #(1,6)#,

#(2,1)#, #(2,2)#, #(2,3)#, #(2,4)#, #(2,5)#, #(2,6)#,
.
.
.
#(6,1)#, #(6,2)#, #(6,3)#, #(6,4)#, #(6,5)#, #(6,6)#.

total #36# possibilities,

of which only #(1,6)#, #(2,5)#, #(3,4)#, #(4,3)#, #(5,2)# and #(6,1)#

i.e. #7# possibilities, result in a sum of #7#.

Hence, probability that you'll roll a sum of #7# is #6/36=1/6#

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