Kwan must read a book that is 400 pages long. He reads at a rate of one page per minute. If he begins reading on a Saturday and he reads one-half hour every day until he finishes the book, on what day of the week will he finish the book?

Kwan reads one page per minute, which means he can read 30 pages in half an hour (since there are 30 minutes in half an hour).

To find out how long it will take him to read a 400-page book at this rate, we can divide the total number of pages by the number of pages he reads each day:

\[
\text{Number of days to finish the book} = \frac{\text{Total pages}}{\text{Pages read per day}} = \frac{400}{30}
\]

Calculating this:

\[
\frac{400}{30} \approx 13.3333
\]

Since he can only read for whole days, we take the ceiling of this value, meaning he will take 14 days to finish the book.

Now, we need to determine the day of the week 14 days after Saturday.

Starting from Saturday:
- 1 day later: Sunday
- 2 days later: Monday
- 3 days later: Tuesday
- 4 days later: Wednesday
- 5 days later: Thursday
- 6 days later: Friday
- 7 days later: Saturday
- 8 days later: Sunday
- 9 days later: Monday
- 10 days later: Tuesday
- 11 days later: Wednesday
- 12 days later: Thursday
- 13 days later: Friday
- 14 days later: Saturday

Thus, Kwan will finish the book on a **Saturday**.