Q3 of 64 Page 122

A candidate is required to answer 7 questions out of 12 questions, which are divided into two groups, each containing 6 questions. He is not permitted to attempt more than 5 questions from either group. Find the number of different ways of doing questions.

Formula: -(i) nCr


No of questions in groupA=6


No of questions in group B=6


The different ways of doing the questions are



(6C2x6C5)+(6C3x6C4)+(6C4x6C3)+(6C5x6C2)


=(15×6)+(20×15)+(15×20)+(6×15)


=780


More from this chapter

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1

Eight chairs are numbered 1 to 8. Two women and 3 men wish to occupy one chair each. First the women choose the chairs from amongst the chairs 1 to 4 and then men select from the remaining chairs. Find the total number of possible arrangements.

 2

If the letters of the word RACHIT are arranged in all possible ways as listed in dictionary. Then what is the rank of the word RACHIT?

[Hint: In each case number of words beginning with A, C, H, I is 5!]

 4

Out of 18 points in a plane, no three are in the same line except five points which are collinear. Find the number of lines that can be formed joining the point.

[Hint: Number of straight lines =18C2 – 5C2 + 1]

 5

We wish to select 6 persons from 8, but if the person A is chosen, then B must be chosen. In how many ways can selections be made?