Question 1205379
On the first round {{{5=5^1 }}}people hear the joke
On the second round, those {{{5 }}}people each tell {{{5 }}}more people, so {{{5*5 = 25 =5^2}}} people hear the joke. 
On the third round, those {{{25}}} people each tell {{{5}}} more people, so {{{25*5 = 125=5^3}}} people hear the joke.
On the fourth round, those {{{125}}} people each tell {{{5}}}more people, so {{{125*5 = 625=5^4 }}}people hear the joke.
On the fifth round, those {{{625}}} people each tell{{{ 5 }}}more people, so{{{ 625*5 = 3125=5^5 }}}people hear the joke.
On the sixth round, those {{{3125}}} people each tell {{{5}}} more people, so {{{3125*5 = 15625=5^6}}} people hear the joke.


expression {{{5^6}}} shows the number of people that will hear the joke after the sixth round


general formula:

{{{y=5^x}}}  where {{{x}}} is the number of rounds and {{{y }}}the number of people hear the joke