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PERMUTATIONS AND COMBINATIONS — MATHS STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceMATHSPERMUTATIONS AND COMBINATIONS2 Marks
Question
Given 4 flags of different colours, how many different signals can be generated, if a signal requires the use of 2 flags one below the other?
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Answer

There will be as many signals as there are ways of filling in 2 vacant places, blank in succession by the 4 flags of different colours. The upper vacant place can be filled in 4 different ways by any one of the 4 flags; we have, the lower vacant place can be filled in 3 different ways by any one of the remaining 3 different flags. Therefore, by the multiplication principle, the required number of signals = 4 $\times$ 3 = 12.

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