Add return on investment to maths

Author: InukaWijerathna

maths/return_on_investment.ts

@@ -0,0 +1,22 @@
+/**
+ * @function returnOnInvestment
+ * @description Calculates Return on Investment (ROI) as a percentage.
+ * ROI measures the profitability of an investment relative to its cost.
+ * Formula: ROI = (Gain - Cost) / Cost * 100
+ * @param {number} gainFromInvestment - Total value gained from the investment
+ * @param {number} costOfInvestment - Total cost of the investment
+ * @return {number} ROI as a percentage
+ * @see https://www.investopedia.com/terms/r/returnoninvestment.asp
+ * @example returnOnInvestment(1000, 500) = 100
+ * @example returnOnInvestment(500, 500) = 0
+ * @example returnOnInvestment(200, 500) = -60
+ */
+export const returnOnInvestment = (
+  gainFromInvestment: number,
+  costOfInvestment: number
+): number => {
+  if (costOfInvestment <= 0) {
+    throw new RangeError('costOfInvestment must be greater than 0')
+  }
+  return ((gainFromInvestment - costOfInvestment) / costOfInvestment) * 100
+}