Question 1195011
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The total number of ways of arranging 3 white marbles and 4 black marbles is<br>
{{{(3+4)!/((3!)(4!)) = 35}}}<br>
With white marbles in the first and last positions, the number of ways of arranging the remaining 1 white marble and 4 black marbles is<br>
{{{(1+4)!/((1!)(4!)) = 5}}}<br>
So the probability that the first and last marbles are both white is 5/35=1/7.<br>