Let the random variable X denote the sum of the two numbers obtained.X can take values between 2 to 12,

P(x=2) = there is only one option first die 1 and second die 1= 1/6*1/6 =1/36

P(x=3) = now there are two options (1,2),(2,1) = 2*(1/6*1/6) = 2/36

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hint

1)total probability = 1

2)draw 6x6 diagram for the sum, to see number of different possibilities for X=x

hope it helps