SATHEE: Permutations And Combinations Question 379

Permutations And Combinations Question 379

Question: Let $ A={x|x $ is prime number and $ x<30} $ . The number of different rational numbers whose numerator and denominator belong to A is

Options:

A) 90

B) 180

C) 91

D) 100

Show Answer

Answer:

Correct Answer: C

Solution:

[c] We have $ A={2,3,5,7,11,13,17,19,23,29} $ A contains 10 elements. So numerator and denominator each can be chosen in 10 ways. So no. of rational numbers $ =10\times 10-10+1=91 $ (Out of these selections, 10 numbers are simply 1)

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Permutations And Combinations Question 379

Question: Let $ A={x|x $ is prime number and $ x<30} $ . The number of different rational numbers whose numerator and denominator belong to A is

Options:

Answer:

Solution:

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