diff --git a/maths/return_on_investment.dart b/maths/return_on_investment.dart
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+/// 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
+///
+/// Reference: https://www.investopedia.com/terms/r/returnoninvestment.asp
+
+double returnOnInvestment(
+    double gainFromInvestment, double costOfInvestment) {
+  if (costOfInvestment <= 0) {
+    throw ArgumentError('costOfInvestment must be greater than 0');
+  }
+  return (gainFromInvestment - costOfInvestment) / costOfInvestment * 100;
+}
+
+void main() {
+  print(returnOnInvestment(1000, 500));  // 100.0
+  print(returnOnInvestment(500, 500));   // 0.0
+  print(returnOnInvestment(200, 500));   // -60.0
+}