First year: 5/( 100-20) = 6.25%

Second year: 5/(80-20) = 8.33%

Third year: 5/(60-20) = 12.5%

Fourth year: 5/(40-20) = 25%

Fifth year: 5/(20-20) = 0%

Algorithm 1: weighted average annual interest rate: (6.25+8.33+12.5+25+0)/5 *100% =10.42% (note: if the merchant directly deducts 200,000 yuan in the first year).

Algorithm two. (Business promotion) Annual interest rate: 250,000/1 10,000 /5 years * 100% = 5%.