Brain Practice Answers

Did these challenges get you thinking?

That’s the objective!

Here are the answers to the March 2021 Brain Practice

Light-Switch Solution

How Many Handshakes?

Six people attended the executive meeting.

Here’s how: The first person to arrive (person A) has no-one to shake hands with. The second to arrive (Person B) has one person to greet. The third person (Person C) has two people to greet and that makes three handshakes.

Person D greets three people (now a total of 6 handshakes) and Person E greets the first four people (that makes 10 handshakes). Person F is the last one in who says Hello to the five people already there and that makes 15 handshakes altogether.

How Many Passes Round the Clock?

Ten times round.

Here’s how:

Many people say ‘eleven’ which is the number of times the minute hand will pass 12 during this 12-hour interval.

But remember that the minute hand is also advancing with each revolution (e.g. the sixth passing of 12 will happen when the hour hand is half way between 6 and 7, not when it is at 6 exactly.)

The tenth – and last – passing occurs when the hour hand is almost touching the 11.

The hands do not pass again before they meet at the stroke of midnight.

What’s the Missing Number?

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