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1) Total number of points in sample space when rolling two four sided dice=4*4=16
    Sum
    probability
    2
    1/16
    3
    2/16
    4
    3/16
    5
    4/16
    6
    3/16
    7
    2/16
    8
    1/16
Probability of getting same sum twice=2*(1/16)^2+2*(2/16)^2+2*(3/16)^2+(4/16)^2
=(2+8+18+16)/256=11/64
                ...............................................
2) Total number of points in sample space when rolling three four sided dice=4*4*4=64
Sum of atleast 9 means 9,10,11,12
    Sum=9
    Total ways
    234
    6
    333
    1
    441
    3
    Total
    10
    Sum=10
    Total ways
    244
    3
    334
    3
    Total
    6
    Sum=11
    Total ways
    344
    3
sum=12        1 ways
Therefore, probability=(10+6+3+1)/64=5/16
                ........................................................
3)
    Sum
    Probability
    3
    1/64
    4
    3/64
    5
    6/64
    6
    10/64
    7
    12/64
    8
    12/64
    9
    10/64
    10
    6/64
    11
    3/64
    12
    1/64
Let p be probability that sum of first roll is greater than second one.
=> P(first roll > second roll) + P(second roll > first roll) +...