Q69 / 180 · COMEDK 2025 (10 May Shift 3) · Mathematics
The number of words that can be formed with the letters of the word 'DEFINITE' if two vowels are together and the other two are also together but separated from the first two is
- A$720$
- B$2880$
- Correct answerC$1440$
- D$1680$
Solution
DEFINITE has 8 letters: Consonants: D, F, N, T (4 distinct); Vowels: E, E, I, I (4 letters with repetition).
The condition requires two groups of 2 vowels each, separated by at least one consonant.
Arrange 4 consonants: $4! = 24$ ways, creating 5 gaps: $\_C\_C\_C\_C\_$
Choose 2 gaps (separated) for the two vowel groups: $\binom{5}{2} = 10$ ways
Arrange 4 vowels (E, E, I, I) in the 4 slots: $\dfrac{4!}{2! \cdot 2!} = \dfrac{24}{4} = 6$ ways
Total $= 24 \times 10 \times 6 = 1440$
The condition requires two groups of 2 vowels each, separated by at least one consonant.
Arrange 4 consonants: $4! = 24$ ways, creating 5 gaps: $\_C\_C\_C\_C\_$
Choose 2 gaps (separated) for the two vowel groups: $\binom{5}{2} = 10$ ways
Arrange 4 vowels (E, E, I, I) in the 4 slots: $\dfrac{4!}{2! \cdot 2!} = \dfrac{24}{4} = 6$ ways
Total $= 24 \times 10 \times 6 = 1440$
Hence, the correct answer is option: 'C'.