Question

given 4 flags of different colours, how many different signals can be generated, if signal requires the use of 2 flags one below the other?

Answer 1

↑ Here is your answer ↓
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Let the color of flags be 'a', 'b', 'c' and 'd',

Now group them,

(a) $ab, ac, ad$

(b) $ba, bc, bd$

(c) $ca, cb, cd$

(d) $da, db, dc$

$= 3 + 3 + 3 + 3$

$= 12$

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