Question

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

A
15
B
11
C
7
D
None of these

Solution

The correct option is C $$7$$Since there are three $$O$$'s. Atleast one '$$O$$' shoilf be there in the selected four letters.Hence there are three cases:$$Case 1:$$  Only one $$O$$ is presentNumber of Selections = 1 (Since we have to select all three remaning letters)$$Case 2:$$ Two $$O$$'s Number of Selections = 3 (two of the remaining 3 letters have to be selected)$$Case 3:$$ Three $$O$$'s Number of Selections = 3 (one of the remaining 3 letters have to be selected)Therefore total number of selections is $$1+3+3=7$$ Maths

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