[harlowe] How to get the "random" command to substract/add a random percentage from a value?

I'm trying to cause it to give me a number stored in $variable1, to which it should either add or substract a random percentage. In this case, something in between -25% and + 25%.

($variable1 + ($variable1 * (random: 0.75,1.25)))

Is there a way to do it?