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Class 11MathematicsPermutations and CombinationsCombinationsEasy
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In how many ways can at least (1) pencil be selected from (7) colored pencils?

Answer and explanation

Correct answer: 127

For each of the 7 pencils, there are two choices: select it or do not select it. Thus, the total number of selections, including the empty selection, is \(2^7=128\). Since at least one pencil must be selected, exclude the empty selection: \(128-1=127\). Option 128 incorrectly includes selecting no pencil. Exam tip: For selections of at least one item from \(n\) distinct items, use \(2^n-1\).

Related tags

CombinationsSubsetsSelection PrinciplesClass 11Permutations And CombinationsMathematicsClass 11 Mcq
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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 \(\frac{10!}{2!\cdot 8!}\times\frac{8}{9}\)?
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