60 words can be made using all the letters of the word $\mathrm{BHBJO}$, with or without meaning. If these words are written as in a dictionary, then the $50^{\text {th }}$ word is:
Solution
<p>To find the $50^{\text{th}}$ word formed by the letters of "BHBJO" as if listed in a dictionary, let's analyze the arrangement methodically. Given the letters are B, H, B, J, O, there are some repetitions with the letter B appearing twice.</p>
<p>First, calculate the total number of permutations of these letters:</p>
<p>$\frac{5!}{2!} = 60$</p>
<p>Let's arrange the letters in alphabetical order first: B, B, H, J, O.</p>
<p>We need to systematically count the words while following dictionary order:</p>
<p>1. Words starting with B:</p>
<ul>
<li>Next position letters: B, H, J, O</li>
<li>Number of permutations: $\frac{4!}{1!} = 24$ words</li>
</ul>
<p>Since 24 words starting with 'B' exist and are less than 50, Move to next starting letter alphabetically.</p>
<p>2. Words starting with H:</p>
<ul>
<li>Next position letters: B, B, J, O</li>
<li>Number of permutations: $\frac{4!}{2!} = 12$ words</li>
</ul>
<p>After 'B', tally becomes 24 (B-words) + 12 (H-words) = 36, needs more.</p>
<p>3. Words starting with J:</p>
<ul>
<li>Next position letters: B, B, H, O</li>
<li>Number of permutations: $\frac{4!}{2!} = 12$ words</li>
</ul>
<p>Now tally is 36 + 12 = 48 words.</p>
<p>Still 2 more to reach 50.</p>
<p>4. Words starting with O:</p>
<ul>
<li>Next position letters: B, B, H, J</li>
<li>Number of permutations: $\frac{4!}{2!} = 12$ words</li>
<li>Our answer must be here since 48 + 2 more = 50 total.</li>
</ul>
<p>First permutation: $OBB H J$</p>
<p>Second permutation (50th word): $OBB J H$</p>
<p>So, the $50^{\text{th}}$ word is: <b>OBBJH</b></p>
<p>Thus, the correct answer is <strong>Option A: OBBJH</strong>.</p>
About this question
Subject: Mathematics · Chapter: Permutations and Combinations · Topic: Fundamental Counting Principle
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