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A fair coin is tossed until the same result turns up in succession(two head or two tail).Find the probability the number of tosses neede are even..

my approach ..P={P(x=2)+P(x=4)+P(x=6)+...}=0.33

what is the reason of this 2 multiplication?

How to get success

Either by HH , HTHH , HTHTHH , HTHTHTHH..........

OR

TT , THTT , THTHTT , THTHTHTT

I guess you took only 1 case.

got that! thanks