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?

Explanation

To solve the problem of how many different signals can be generated using 2 flags from a set of 4 flags of different colors, we can follow these steps:

### Step 1: Identify the total number of flags
We have a total of 4 flags, each of a different color.

### Step 2: Determine the arrangement of flags
Since the flags are to be arranged one below the other, we need to select 2 flags and arrange them in a specific order (the first flag will be on top and the second flag will be below).

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