The dog ate my homework!

1

• The dog ate my homework!
• A certain teacher, Mr L I Detector, claims he can
  tell when students are lying about their
  homework.
• This is true.
• Unfortunately, he also accuses some students who
  are telling the truth.
• So what are the chances that someone will be
  wrongly accused?

2

• Form yourself into groups of 4 or 5, and collect
• a die
• some red, blue, green and yellow cubes
• a worksheet

3

• Throw the die.

I am telling the truth!
Im not telling the truth!
Anything else

4

• Throw the die.
• Who needs to throw the die again to find out what
  Mr D thinks?
• Who doesnt?

I am telling the truth!
Im not telling the truth!
Anything else

5

• Throw the die.
• Who needs to throw the die again to find out what
  Mr D thinks?
• Who doesnt?
• If the student was lying, then Mr D knows, so
  there is no need to throw the die again.

I am telling the truth!
Im not telling the truth!
Anything else

Mr D accuses me!
?
6

• If the student is not lying, throw the die again.

I am telling the truth!
7

• If the student is not lying, throw the die again.

I am telling the truth!
Its not fair! Mr D accuses me!

?
8

• If the student is not lying, throw the die again.

I am telling the truth!
Phew! He doesnt accuse me!
Its not fair! Mr D accuses me!
Anything else

?
?
9

• The experiment
• Repeat the experiment 36 times.
• First throw of die
• Second throw of die (if needed)

The dog ate my homework! A certain teacher, Mr L
I Detector, claims he can tell when students are
lying about their homework. This is
true. Unfortunately, he also accuses some
students who are telling the truth. So what are
the chances that someone will be wrongly accused?
Im not telling the truth!
?

I am telling the truth!
Anything else
Its not fair! Mr D accuses me!

Phew! He doesnt accuse me!
Anything else
10

• So what are the chances that someone will be
  wrongly accused?
• What does the evidence of the cubes suggest?
• Are you surprised by what you see?

11

• So what are the chances that someone will be
  wrongly accused?
• What does the evidence of the cubes suggest?
• Are you surprised by what you see?
• Complete the tree diagram and 2-way table for
  your results, then add your cubes to the
  collective 2-way table.
• Complete the tree diagram and 2-way table for
  what you would EXPECT to happen.
• How do your results compare?
• How about the collective results for the whole
  class?