A) 15
B) 11
C) 7
D) None of these
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.
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