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Correct Answer: 5:43 and 7/11​ minutes

Let $h$ be the hour and $m$ be the minutes. The hour hand moves $360^\circ$ in 12 hours, or $30^\circ$ per hour, or $0.5^\circ$ per minute. The minute hand moves $360^\circ$ in 60 minutes, or $6^\circ$ per minute.

We are looking for the time between 5:30 and 6:00, so $h=5$ and $30 \le m < 60$. The position of the hour hand at time $h:m$ is $30h + 0.5m$ degrees. The position of the minute hand at time $h:m$ is $6m$ degrees.

We want the hands to be at right angles, so the difference in their positions is $90^\circ$ or $270^\circ$. Case 1: $6m - (30h + 0.5m) = 90$ $6m - 30(5) - 0.5m = 90$ $5.5m - 150 = 90$ $5.5m = 240$ $m = \frac{240}{5.5} = \frac{2400}{55} = \frac{480}{11} = 43\frac{7}{11}$ So the time is $5:43\frac{7}{11}$. Since $30 \le 43\frac{7}{11} < 60$, this is a valid solution.

Case 2: $6m - (30h + 0.5m) = -90$ $6m - 30(5) - 0.5m = -90$ $5.5m - 150 = -90$ $5.5m = 60$ $m = \frac{60}{5.5} = \frac{600}{55} = \frac{120}{11} = 10\frac{10}{11}$ This time is $5:10\frac{10}{11}$, which is not between 5:30 and 6.

Case 3: $30h + 0.5m - 6m = 90$ $30(5) + 0.5m - 6m = 90$ $150 - 5.5m = 90$ $5.5m = 60$ $m = \frac{60}{5.5} = \frac{600}{55} = \frac{120}{11} = 10\frac{10}{11}$ This time is $5:10\frac{10}{11}$, which is not between 5:30 and 6.

Case 4: $30h + 0.5m - 6m = -90$ $30(5) + 0.5m - 6m = -90$ $150 - 5.5m = -90$ $5.5m = 240$ $m = \frac{240}{5.5} = \frac{2400}{55} = \frac{480}{11} = 43\frac{7}{11}$ So the time is $5:43\frac{7}{11}$. Since $30 \le 43\frac{7}{11} < 60$, this is a valid solution.

So the only time between 5:30 and 6 is $5:43\frac{7}{11}$.

Final Answer: The final answer is $\boxed{5:43:42}$

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Prompt: At what time between 5.30 and 6 will the hands of a clock be at right angles?

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