The Duckworth-Lewis method (D/L method) is a mathematical way to calculate the target score for the team batting second in a one-day cricket or Twenty-20 cricket match interrupted by weather or other circumstance.
The D/L method was devised by two English statisticians, Frank Duckworth and Tony Lewis.
Theory of Duckworth-Lewis Method
Website of Duckworth - Lewis Method
Duckworth Lewis Method Online Calculator