How long does it take to call fifty students at most in the primary school math book?

Solution: Suppose it takes 1 minute to make a phone call.

Then: it takes 6 times to notify 50 people, that is:

When one person knows, call the second person. At this time, * * * two people know (1 person notification 1 minute).

Two people call each other separately, and at this time * * * four people know (two people call 1 minute).

Four people call each other separately, and then * * * eight people know (four people call 1 minute).

Eight people call each other separately, and then * * * sixteen people know (eight people call 1 minute).

16 people call each other separately, and at this time * * * 32 people know (16 people call 1 minute).

At this time, there are still 18 people who don't know. Ask 18 people who know to notify again (18 people to notify 1 minute).

Because they are all carried out at the same time, it will take at least 6 minutes to inform everyone.