Solving problems with linear equations of one variable. Clocks and watches are timing tools in daily life. By observing clocks and watches, we can find many interesting math problems?
15:00, the minute hand and the hour hand form a 90-degree angle, then the hour hand slowly advances at a speed of 0.5/ minute, and the minute hand catches up at a speed of 6/ minute. When the distance between the minute hand and the hour hand is 13, the minimum elapsed time t satisfies 6t-0.5t=90- 13.
Simplified to 5.5t=77,
T=77/5.5= 14 minutes.