+def percentage_to_multiplier(percent: float) -> float:
+ """Given a percentage (e.g. 155%), return a factor needed to scale a
+ number by that percentage.
+
+ >>> percentage_to_multiplier(155)
+ 2.55
+ >>> percentage_to_multiplier(45)
+ 1.45
+ >>> percentage_to_multiplier(-25)
+ 0.75
+
+ """
+ multiplier = percent / 100
+ multiplier += 1.0
+ return multiplier
+
+
+def multiplier_to_percent(multiplier: float) -> float:
+ """Convert a multiplicative factor into a percent change.
+
+ >>> multiplier_to_percent(0.75)
+ -25.0
+ >>> multiplier_to_percent(1.0)
+ 0.0
+ >>> multiplier_to_percent(1.99)
+ 99.0
+
+ """
+ percent = multiplier
+ if percent > 0.0:
+ percent -= 1.0
+ else:
+ percent = 1.0 - percent
+ percent *= 100.0
+ return percent
+
+