AP EAMCET Engineering 18 Sep 2020 Shift 1 Paper

There are two dice A and B . Die A has 4 red and 2 white faces and B has 2 red and 4 white faces. A coin is tossed once, if it shows head, die A is rolled, if it shows tail, die B is rolled if the probability that die A is used is (

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) when it is given that red turns up every time in first n throws, then n=