dse 2010 q4

[sneha]

A fair coin is tossed repeatedly untill a head is obtained for the first time. Let X denoted  the no. of tosses that are required.what is the value of the distribution function of X at 3?

[duck]

Hi.. :)

They are asking you to find out P[x<= 3] =P[x=1]+ P[x= 2] + P[x= 3]
                                                        =1/2 + 1/4 + 1/8
                                                        = 7/8