-f is a binary operator that takes a format string as it's left operand and an array of values to format as it's right operand.
https://devcentral.f5.com/articles/powershell-abcs-f-is-for-format-operator#.UtbRQWRDuHw
http://www.computerperformance.co.uk/powershell/powershell_-f_format.htm
"{0:n2}% " -f
ddd
dddd