33,800,000 are total distinct six characters license plates possible such that the two letters must appear next to each other. We can solve it by using combination formula ( ⁿCr ) .
Total number of digits are 10 i.e., 0,1,2,3,4,5,6,7,8,9. We have given the option to select any four digits out of 10 with repetition. So, we use combination formula
ⁿ C r = n!/(r! ×(n-r)! )
For 1ˢᵗ digit, the number ways to choose the 1ˢᵗ digit is ¹⁰C ₁= 10
For 1ˢᵗ letter, the number of ways to choose the 1ˢᵗ letter is ²⁶C ₁= 26
There are 10×10×10×10 = 10⁴ ways to choose four digits . In a similar way, the total number of letters for choice is 26 ; i.e., from A to Z. We were given the task of choosing two letters from a list of 26 , which were not necessarily distinct .
There are 26×26 = 26²ways to choose the two letters . For the letters to be next to each other, they can be the 1ˢᵗ and 2ⁿᵈ, 2ⁿᵈand 3ʳᵈ, 3ʳᵈand 4ᵗʰ, 4ᵗʰand 5ᵗʰ, 5ᵗʰ and 6ᵗʰ characters . So, there are 6-1 = 5 are choices for the positions of the letters .
Therefore, numbers of distinct license plates is 5×10⁴× 26² = 33,800,000
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