7.1.2 Let X , Y have the joint distribution given by the following table:

X I Y 2 3 4

- b 0 4l8 0 O 48 8

48 11

-5 -

a 1

2 3

- 0 48 48 O 5 12 48

- -

(i) Find a and b if it is known that P ( X = Y ) = 1/3. (ii) Find P ( X Y = 0).

(iii) If F is the cdf of ( X , Y ) , find F(-1.5,3), F(0.7,2.11),and F(1.5,18).