Quick questions on Credit card interest, daily compounding and the cost of revolving debt for HSC Maths Standard 2

A daily-compounded rate has a slightly higher effective annual rate than the nominal rate, because the interest itself earns interest through the year:

Cards usually require a minimum monthly repayment of about $2$-$3\%$ of the closing balance (or a small fixed amount such as $25, whichever is greater). The trap is just arithmetic. The monthly interest on a typical card is itself close to that same percentage. So the minimum payment barely clears more than the interest, and the balance falls at a crawl.

A typical statement period is one month. Interest is worked out daily on the balance and added to the account at the end of the statement period. That added interest then earns interest itself the next period. This is what makes it compounding rather than simple.

Count actual calendar days, not weeks or months. February has $28$ days, not $30$.

Use the daily rate $R/365$ for daily compounding, then raise to the number of days.