KVPY SX SB Exam 20141 Question Paper

Question : 15 of 120

Marks: +1, -0

Two persons A and B throw a (fair) die (six-faced cube with faces numbered from 1 to 6) alternately, starting with A . The first person to get an outcome different from the previous one by the opponent wins. The probability that B wins is

$5/6$
$6/ 7$
$7/8$
$8/ 9$

Validate

Solution:

P=6/6 . 5/6 +6/6 . 1/6 . 1/6 . 5/6+6/6 . 1/6 . 1/6 . 1/6 . 1/6 . 5/6+...∞

=5/6+5/6^3+5/6^5+....

={5\/6}/{1-1/36}=30/35=6/7

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