SATHEE: Permutations And Combinations Question 280

Permutations And Combinations Question 280

Question: The number of 5 digit telephone numbers having at least one of their digits repeated is [Pb. CET 2000]

Options:

A) 90,000

B) 100,000

C) 30,240

D) 69,760

Show Answer

Answer:

Correct Answer: D

Solution:

Using the digits 0, 1, 2, ……, 9 the number of five digit telephone numbers which can be formed is $ 10^{5} $ (since repetition is allowed) The number of five digit telephone, numbers which have none of the digits repeated = $ ^{10}P_5=30240 $ .
$ \therefore $ The required number of telephone numbers = $ 5\times 4=20 $ .

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Permutations And Combinations Question 280

Question: The number of 5 digit telephone numbers having at least one of their digits repeated is [Pb. CET 2000]

Options:

Answer:

Solution:

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