How many 7-letter words consisting of exactly 4 consonants and 3 vowels can be formed from 12 distinct consonants and 4 distinct vowels if the first 4 positions are consonants and the last 3 positions are vowels (pattern C C C C V V V)?

Difficulty: Medium

Correct Answer: 285120

Explanation:


Introduction / Context:
The original options suggest a fixed-position pattern for consonants and vowels rather than free intermixing. We will explicitly adopt the pattern C C C C V V V to avoid ambiguity and align with the given numeric scale.


Given Data / Assumptions:

  • 12 distinct consonants available; choose and arrange 4 into the first four slots.
  • 4 distinct vowels available; choose and arrange 3 into the last three slots.
  • All letters are distinct; within each block, order matters.


Concept / Approach:
Number of choices for consonant block = 12P4. Number for vowel block = 4P3. Multiply blocks because they are independent under the fixed pattern.


Step-by-Step Solution:

Consonant block (C C C C): 12P4 = 1211109 = 11880.Vowel block (V V V): 4P3 = 43*2 = 24.Total words = 11880 * 24 = 285120.


Verification / Alternative check:
If consonants and vowels could appear in any positions (not fixed), the count would be 12C4 * 4C3 * 7!, which equals 9,979,200—far larger and inconsistent with the provided options. Hence the fixed-slot interpretation is appropriate.


Why Other Options Are Wrong:
251820, 258120, 281520 are near-misses derived from arithmetic slips or using combinations instead of permutations in one of the blocks.


Common Pitfalls:
Mixing up P and C; using 12C4 or 4C3 in place of 12P4 or 4P3 when the within-block order matters.


Final Answer:
285120

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