\(x_1+x_2+x_3=19\) में \(0\leq x_i\leq7\) हो, तो valid count किस expression से मिलेगा?
If \(x_1+x_2+x_3=19\) and \(0\leq x_i\leq7\), which expression gives the valid count?
Explanation opens after your attempt
A. \(^{21}C_2-3{}^{13}C_2+3{}^{5}C_2\)
Concept
The upper violation is \(x_i\geq8\) and inclusion-exclusion is applied. In exams use shift (8) for upper bound (7).
Why this answer is correct
The correct answer is A. \(^{21}C_2-3{}^{13}C_2+3{}^{5}C_2\). The upper violation is \(x_i\geq8\) and inclusion-exclusion is applied. In exams use shift (8) for upper bound (7).
Exam Tip
Upper violation \(x_i\geq8\) है और inclusion-exclusion applied होता है। परीक्षा में upper bound (7) के लिए shift (8) लें।
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