For "Fast Calculations"
A "fast calculation formula" is often helpful at the arrival in Sri Lanka, in order to know e.g. how much tip to give to the luggage boy or driver.
1US-$ is worth around 100 Rupee. When giving a tip you preferably give the same amount that you would give back home, e.g. if at home you give €3, here you should give 300 Rupees. Please remember that this is only a "fast calculation formula" and not the real exchange rate that you get at the airport or at the Lotus-Villa.