The currency of Georgia is called the Lari (GEL), and when I visited in July 2019, the conversion rate was 1 USD = 2.8794 GEL. Because everything was priced in GEL but I think about prices in USD, I had to convert prices every time I wanted to buy something. It would have been tiring to pull out a calculator for every single purchase, so I wanted a way to estimate how much things cost.

The rule I came up with was the following: round the price up to the next highest multiple of 3, and then divide by 3. I wanted to round to a multiple of 3 to make the calculations easier to do in my head, but I specifically chose to round up because the exchange rate was slightly worse than 3:1. If I had just divided by 3, I would have been under-estimating prices. So rounding up would help to account for that. Let's see how accurate this method worked:

One of my favorite dishes in Georgia was adjarian khachapuri, which was basically a bread bowl filled with cheese, a slab of butter, and a raw egg. You mix the ingredients together, and the hot cheese cooks the egg, creating a fatty, delicious filling. I ordered a khachapuri for lunch one day, and it cost 8.5 GEL. To estimate the cost in USD, I rounded up to the next multiple of three (which would be 9), and then I divided by three, which gave me a price of 3 USD. So I knew that the cost was approximately 3 USD. To find the exact cost, I could divide the cost in GEL by the conversion rate of 2.8794 to get a price of $2.95. Not bad - I was only five cents off!

Next, let's estimate the cost of my hostel. The price was 35 GEL per night. If we round this up to the next multiple of three, we get 36. Then, dividing this by three gives us 12 USD. To find the exact cost, we divide 35 by 2.8794 to get $12.16. This time I was only 16 cents off.

Sample Problems

1. It cost me 5 GEL to ride the Ferris wheel at the Mtatsminda Amusement Park. Estimate the cost in USD, calculate the exact cost, and determine how far off the estimation was.

2. It cost me 49 GEL to take a day trip out of the Georgian capital of Tbilisi. Estimate the cost in USD, calculate the exact cost, and determine how far off the estimation was.

3. It cost me 15 GEL to enter the Stalin Museum in Gori. Estimate the cost in USD, calculate the exact cost, and determine how far off the estimation was.

4. Which of these estimations were over-estimates, and which were under-estimates? Can you determine a rule for when an estimate will be too high or too low?