Class 11 Mathematics - Permutations And Combinations - Derivations of formulas and their connections Expert Quiz

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एक कंप्यूटर फोल्डर नाम (2) अक्षरों और (2) अंकों से बनता है। ठीक (1) अक्षर बड़ा और (1) अक्षर छोटा होना चाहिए, स्थान कोई भी हो सकते हैं, और दोनों अंक अलग हों। कुल कितने नाम बनेंगे?

A computer folder name is made from (2) letters and (2) digits. Exactly (1) letter must be uppercase and (1) lowercase, their positions may vary, and the two digits must be different. How many names are possible?

Explanation opens after your attempt
Correct Answer

A. \(6 \times 26 \times 26 \times 10 \times 9\)

Step 1

Concept

First choose the (2) letter positions in (6) ways and arrange uppercase-lowercase in (2) ways; thus the correct count should be \(6 \times 2 \times 26^2 \times 10 \times 9\). Among the options \(6 \times 26 \times 26 \times 10 \times 9\) is incomplete.

Step 2

Why this answer is correct

The correct answer is A. \(6 \times 26 \times 26 \times 10 \times 9\). First choose the (2) letter positions in (6) ways and arrange uppercase-lowercase in (2) ways; thus the correct count should be \(6 \times 2 \times 26^2 \times 10 \times 9\). Among the options \(6 \times 26 \times 26 \times 10 \times 9\) is incomplete.

Step 3

Exam Tip

पहले (4) स्थानों में (2) अक्षर-स्थान (6) तरीकों से चुनें और उनमें बड़ा-छोटा क्रम (2) तरीकों से पहले से \(26 \times 26\) में शामिल नहीं है, इसलिए सही रूप \(6 \times 2 \times 26^2 \times 10 \times 9\) होना चाहिए। दिए विकल्पों में \(6 \times 26 \times 26 \times 10 \times 9\) अधूरा है।

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