(7) अलग-अलग पेन में से (4) पेन को क्रम से रखने के तरीके कितने हैं?
How many ways are there to arrange (4) pens selected from (7) different pens in order?
Explanation opens after your attempt
A. (840)
Concept
\({}^{7}P_{4}=7\times6\times5\times4=840\). For (r) places, multiply (r) decreasing factors.
Why this answer is correct
The correct answer is A. (840). \({}^{7}P_{4}=7\times6\times5\times4=840\). For (r) places, multiply (r) decreasing factors.
Exam Tip
\({}^{7}P_{4}=7\times6\times5\times4=840\)। (r) स्थानों के लिए (r) घटते गुणनखंड लें।
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