Answer
424.5k+ views
Hint: Consider it as an 8 blank spaces \[----\] as the 8 outcomes of the coupon, on each blank space we can assign 4 numbers T, I, D, E. Now If he gets exactly one free packet.
It means we want complete T I D E word to be formed only one time
So, we assign it like T I D E \[--\] now we just have to perform permutation on blanks
Complete step-by-step answer:
Now like we have 8 coupons means 8 outcomes and, on each coupon, we can get 4 characters T, I, D, E but we get exactly one free packet, so it means complete TIDE word will be formed only one time
T I D E \[--\]
Now we can perform permutation on blank, each of the 4 blanks have 4 options T, I, D, E
so, we write it as \[{{x}_{1}}+{{x}_{2}}+{{x}_{3}}+{{x}_{4}}=4......(1)\]
here \[{{x}_{1}},{{x}_{2}},{{x}_{3}},{{x}_{4}}\] denotes the number of T, I, D, E we take in blank spaces in different permutations,
where \[1\le {{x}_{1}},{{x}_{2}},{{x}_{3}},{{x}_{4}}\le 8\]
Then the required number of combinations of coupons is equivalent to the number of positive integral solutions of the equation (1),
Using formula
\[{{x}_{1}}+{{x}_{2}}+{{x}_{3}}.....+{{x}_{r}}=n\] total permutations will be \[{}^{n+r-1}{{c}_{r-1}}\]
On applying this formula to equation (1)
Our total permutation will be \[{}^{4+4-1}{{c}_{4-1}}\]
\[\to {}^{7}{{c}_{3}}\]
So, our final answer is \[{}^{7}{{c}_{3}}\]
So, the correct answer is “Option A”.
Note: We assigned like this T I D E \[--\]
But most of you might have doubt that why we didn’t count permutation of
T I D E word as \[4!\] , because it doesn’t matter whether I got T I D E or E, D, I, T or I, T, D, E. In total we just want to make a complete word.
It means we want complete T I D E word to be formed only one time
So, we assign it like T I D E \[--\] now we just have to perform permutation on blanks
Complete step-by-step answer:
Now like we have 8 coupons means 8 outcomes and, on each coupon, we can get 4 characters T, I, D, E but we get exactly one free packet, so it means complete TIDE word will be formed only one time
T I D E \[--\]
Now we can perform permutation on blank, each of the 4 blanks have 4 options T, I, D, E
so, we write it as \[{{x}_{1}}+{{x}_{2}}+{{x}_{3}}+{{x}_{4}}=4......(1)\]
here \[{{x}_{1}},{{x}_{2}},{{x}_{3}},{{x}_{4}}\] denotes the number of T, I, D, E we take in blank spaces in different permutations,
where \[1\le {{x}_{1}},{{x}_{2}},{{x}_{3}},{{x}_{4}}\le 8\]
Then the required number of combinations of coupons is equivalent to the number of positive integral solutions of the equation (1),
Using formula
\[{{x}_{1}}+{{x}_{2}}+{{x}_{3}}.....+{{x}_{r}}=n\] total permutations will be \[{}^{n+r-1}{{c}_{r-1}}\]
On applying this formula to equation (1)
Our total permutation will be \[{}^{4+4-1}{{c}_{4-1}}\]
\[\to {}^{7}{{c}_{3}}\]
So, our final answer is \[{}^{7}{{c}_{3}}\]
So, the correct answer is “Option A”.
Note: We assigned like this T I D E \[--\]
But most of you might have doubt that why we didn’t count permutation of
T I D E word as \[4!\] , because it doesn’t matter whether I got T I D E or E, D, I, T or I, T, D, E. In total we just want to make a complete word.
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