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# How Old Am I?

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Age 14 to 16

Challenge Level

*How Old Am I? printable worksheet *

On my last birthday, my friend said to me:

"In 15 years' time, your age will be the square of your age 15 years ago!"

**Can you work out how old I am?**

This got me thinking...

**Was there ever a time in my life when I had other birthdays that were special in this way?**

Could I have said:

"In 3 years' time, my age will be the square of my age 3 years ago"

or:

"In 4 years' time, my age will be the square of my age 4 years ago"

or:

"In 5 years' time, my age will be the square of my age 5 years ago"

or:

"In 6 years' time, my age will be the square of my age 6 years ago"

or...?

**Can you make any generalisations about which birthdays are special in this way?
Can you prove your findings?**

Click here for a poster of this problem.

Rectangle PQRS has X and Y on the edges. Triangles PQY, YRX and XSP have equal areas. Prove X and Y divide the sides of PQRS in the golden ratio.

Two cubes, each with integral side lengths, have a combined volume equal to the total of the lengths of their edges. How big are the cubes? [If you find a result by 'trial and error' you'll need to prove you have found all possible solutions.]

Is the mean of the squares of two numbers greater than, or less than, the square of their means?