Permutations And Combinations Question 143

Question: The number of ways in which any four letters can be selected from the word ?CORGOO? is

Options:

A) 15

B) 11

C) 7

D) None of these

Show Answer

Answer:

Correct Answer: C

Solution:

  • Four letters can be selected in the following ways (i) All different $ i.e. $ $ C,\ O,\ R,\ G $ . (ii) 2 like and 2 different. (iii) 3 like and 1 different $ i.e. $ three $ O $ and 1 from R, G and C. The number of ways in (i) is $ ^{4}C_4=1 $ The number of ways in (ii) is $ 1\ .{{\ }^{3}}C_2=3 $ The number of ways in (iii) is $ 1{{\times }^{3}}C_1=3 $ Therefore, required number of ways = $ 1+3+3= $ 7.