How many $8-$digit telephone numbers can be constructed using the digits $0$ to $9$ if each number starts with $270$ and $n$ digit appears more than once?

A coin is tossed three times and the outcomes are recorded. How many possible outcomes are there?

How many possible outcomes if the coin is tossed four times?

How many possible outcomes if the coin is tossed five times?

If $k^n$ is possible outcomes if the coin is tossed $n$ times, then $k=$

Find the number of different signals that can be generated by arranging at least $2$ flags in order (one below the other) on a vertical staff, if five different flags are available.