अंग्रेज़ी वर्णमाला में $5$ स्वर तथा $21$ व्यंजन हैं। इस वर्णमाला से $2$ भिन्न स्वरों और $2$ भिन्न व्यंजनो वाले कितने शब्दों की रचना की जा सकती है ?

$2$ different vowels and $2$ different consonants are to be selected from the English alphabet. since there are $5$ vowels in the English alphabet, number of ways of selecting $2$ different vowels from the alphabet $=\,^{5} C_{2}=\frac{5 !}{2 ! 3 !}=10$

since there are $21$ consonants in the English alphabet, number of ways of selecting $2$ different consonants from the alphabet $=\,^{21} C_{2}=\frac{21 !}{2119 !}=210$

Therefore, number of combinations of $2$ different vowels and $2$ different consonants $=10 \times 210=2100$

Each of these $2100 $ combinations has $4$ letters, which can be arranged among themselves in $4 !$ ways.

Therefore, required number of words $=2100 \times 4 !=50400$