Muft Shiksha
Update

Muft Shiksha™ एक 100% Free Education Portal है 🇮🇳, जिसका उद्देश्य Class 9–12 के हर विद्यार्थी तक High-Quality Education को पूरी तरह मुफ्त पहुँचाना है। 🇮🇳 हम मानते हैं कि अच्छी शिक्षा किसी student की आर्थिक स्थिति पर निर्भर नहीं होनी चाहिए। 🇮🇳 हर विद्यार्थी को वही Quality Study Material, MCQs, Quizzes, Exam Preparation, Concept-Based Learning और Bilingual Support मिलना चाहिए, जो आमतौर पर महंगी Coaching या Premium Platforms में मिलता है। Muft Shiksha™ 🇮🇳 इसी सोच के साथ बनाया गया है

Subjects
Class 11MathematicsPermutations and CombinationsCombinationsEasy
0 reads0 ratings0 helpful

From (8) different keys, (2) keys are to be selected and one particular key must not be selected. How many ways are there?

Answer and explanation

Correct answer: 21

First exclude the particular key that must not be selected. This leaves 7 keys, and the number of ways to choose 2 of them is \(\binom{7}{2}=\frac{7\times6}{2}=21\). Using \(\binom{8}{2}=28\) would incorrectly include selections containing the prohibited key. Exam tip: for a “must not be selected” condition, remove that object before forming the combination.

Related tags

CombinationsPermutations And CombinationsClass 11Restricted SelectionBinomial CoefficientMathematicsClass 11 Mcq
सुधार सुझाएँ / Earn

Was this question useful?

No ratings yetWrite a review / Rate this question

Student Reviews

No published reviews yet.

KEEP PRACTISING

10 more MCQs
  1. 1A shop has 6 different types of pencils and 2 different types of notebooks. In how many different ways can one pencil and one notebook be bought?
  2. 2A student chooses one subject from 3 subjects and one game from 5 games. How many different selections are possible in total?
  3. 3There are 4 bus routes and 3 train routes from a city to a village. In how many different ways can the journey be made using exactly one mode of transport?
  4. 4An examination contains 6 short-answer questions and 4 long-answer questions. A student has to solve exactly one of them. In how many ways can the student choose the question?
  5. 5A meal plate offers 2 bread choices, 3 vegetable choices, and 2 dessert choices. In how many ways can a plate be prepared by choosing one item from each category?
  6. 6A bag contains pens in 3 different colors, markers in 4 different colors, and pencils in 2 different colors. In how many ways can one pen, one marker, and one pencil be chosen?
  7. 7A vehicle number consists of two letters followed by two digits. There are 4 choices for each letter and 10 choices for each digit. If repetition of letters and digits is allowed, how many distinct vehicle numbers can be formed?
  8. 8A bag has 6 red and 5 blue balls. Four balls are to be selected with equal numbers of both colours. How many selections are possible?
  9. 9If \(\frac{(n+2)!}{(n-2)!}=3024\), what is the value of \(n\)?
  10. 10What is the value of \(\frac{10!}{2!\cdot 8!}\times\frac{8}{9}\)?
Found an issue? Help improve this questionMy reports and replies

Add Muft Shiksha to your Home Screen

In Safari, tap Share, then Add to Home Screen.