Permutations And Combinations Question 256

Question: The sum of the digits in the unit place of all numbers formed with the help of 3, 4, 5, 6 taken all at a time is [Pb. CET 1990]

Options:

A) 18

B) 432

C) 108

D) 144

Show Answer

Answer:

Correct Answer: C

Solution:

  • Required sum $ =3\ !(3+4+5+6)=6\times 18=108 $ . [If we fix 3 of the unit place, other three digits can be arranged in $ 3\ ! $ ways similarly for 4, 5, 6.]

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