1. **State the problem:** You want to borrow 800 for four weeks, and the interest is 10 per 100 borrowed. We need to find the APR (Annual Percentage Rate). 2. **Understand the formula:** APR is the annualized interest rate. The interest for 4 weeks is given, so we first find the interest rate for 4 weeks, then annualize it. 3. **Calculate the interest rate for 4 weeks:** Interest per 100 borrowed = 10 For 800 borrowed, interest = $10 \times \frac{800}{100} = 80$ 4. **Calculate the interest rate for 4 weeks:** $$\text{Interest rate for 4 weeks} = \frac{80}{800} = 0.1 = 10\%$$ 5. **Annualize the interest rate:** There are 52 weeks in a year, so number of 4-week periods in a year = $\frac{52}{4} = 13$ 6. **Calculate APR:** $$\text{APR} = 10\% \times 13 = 130\%$$ **Final answer:** The APR at which you are borrowing money is **130%**.