In the Indian System of Numeration, 'Five crore twenty-three lakh forty-five thousand six hundred seventy-eight' is written as 5,23,45,678. To convert this to the International System, we consider the place values. 1 crore is equal to 10 million, and 1 lakh is equal to 100 thousand. So, 5 crore = 50 million, and 23 lakh = 2.3 million. Combining these, the number becomes 50 million + 2.3 million + 45 thousand + 678, which is 52,345,678. In the International System, numbers are grouped in threes from the right (e.g., thousands, millions, billions). Hence, 52,345,678 is the correct representation.