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# Litov's Mean Value Theorem

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Age 11 to 14

Challenge Level

*Litov's Mean Value Theorem printable sheet*

**Start with two numbers, say 8 and 2.**

Let's generate a sequence where the next number is the mean of the previous two numbers.

So the next number is half of $(8 + 2)$, and the sequence continues: $8, 2, 5$

The next number is half of $(2 + 5)$, and the sequence continues: $8, 2, 5, 3.5$

**What would happen if you continued this process indefinitely?**

Choose a few pairs of starting numbers and repeat the process.

Each time, your sequence should get closer and closer to a value which we call the *limit*.

**Can you find a relationship between your starting numbers and the limit of the sequence they generate?**

Can you explain why this happens?

Now start with three numbers.

This time, we can generate a sequence where the next number is the mean of the last three numbers.

Check you agree that if we start with $4, 1, 10$, the next number is 5, and the number after that is $\frac{16}{3}$.

**What would happen if you continued this process indefinitely?**

Choose some more sets of three starting numbers.

**Can you find a relationship between your starting numbers and the limit of the sequence they generate?**

Can you explain why this happens?

Extension

Explore what happens when you have $n$ starting numbers and you generate a sequence where the next number is the mean of the last $n$ numbers.

Two students collected some data on the wingspan of bats, but each lost a measurement. Can you find the missing information?

When Kate ate a giant date, the average weight of the dates decreased. What was the weight of the date that Kate ate?

How many visitors does a tourist attraction need next week in order to break even?