Frequenz read and reduce it 20% as an output signal

[sasa23]

Hello guys,

i´m looking for some help, how to ready out an variable frequenz and reduce it always -20%.
To ready out fequnet and duty cycle i can find a lot of example, but to give out an signal output with 20% reduced from the input signal can´tfind it.

Any help?`

thanks
SASA

[Idahowalker]

SomeNumber * .8 = 20%lessThanSomeNumber.