'Exchange Rates and Interest Calculated' Middle School Daughter Presents Overdue Allowance Invoice... Father's Reaction?

Japanese Kagoshima 1st Grader's 10-Page Invoice Sparks Attention
Calculates Potential Losses Considering Interest Rate and Exchange Rate Fluctuations
Wins Top Prize at Local Math and Arithmetic Research Contest

Chizuru Kawahara, a first-year student at Kagoshima University Attached Junior High School in Kagoshima City, Japan, handed her father Masayuki Kawahara (44) a bill last summer. It was a so-called overdue allowance bill. Chizuru had not received the allowance promised by her father every month for 17 months, from April of her sixth grade in elementary school to September of her first year in junior high school. Whenever she reminded him, he would just say, "Okay."

Chizuru began to research, thinking she should be more persuasive and receive more for the overdue amount. The originally promised monthly allowance was 500 yen (4,500 won) during elementary school and 1,000 yen (9,100 won) from junior high school. Calculating for 17 months, it amounted to 11,000 yen (103,000 won). However, this was just the principal. Since 17 months were overdue, she thought she should not receive only this amount.

Starting with the principal of 11,000 yen, she investigated and verified interest rates and exchange rates for two types of deposits: fixed-term deposits and foreign currency deposits. The interest rate was extremely low for fixed deposits, resulting in almost no change, while foreign currency deposits increased but had unpredictable exchange rates. Next, she focused on the late payment damages that could be claimed when payment was delayed. Assuming an annual rate of 20%, the legal maximum, the delay damages for 17 months of arrears amounted to 1,404 yen (12,800 won), which was the highest among the three methods. Therefore, she decided to claim a total amount of 12,404 yen (113,000 won), including the principal.

Research by a Japanese first-year middle school girl who directly calculated and proved potential losses due to delayed debt, that is, delayed interest.
[Image source=Isu Education Research Institute]

Chizuru created a "thesis" titled "Issuing a Bill to My Father," organized into 10 pages on A4 paper using tables and graphs. She submitted the thesis to the 11th Mathematics and Arithmetic Independent Research Contest hosted by the Japan Institute of Educational Research and won the top prize. The judges commented, "This was the result of a desperate wish for the allowance her father did not give her," and praised the strategy of issuing a bill by calculating the return amounts for fixed deposits, foreign currency deposits, and late payment damages on the claim. They also noted the freshness, realism, and seriousness conveyed by a junior high school student calculating interest on money by herself."

Her father, who received the bill, said he was "speechless because there was nothing to criticize." Thanks to her diligent research, Chizuru was able to receive the overdue allowance from her father. She also said, "These days, the allowance is again overdue, so next time I will think of another way to claim it."

This content was produced with the assistance of AI translation services.