### Pebbles

Place four pebbles on the sand in the form of a square. Keep adding as few pebbles as necessary to double the area. How many extra pebbles are added each time?

### Great Squares

Investigate how this pattern of squares continues. You could measure lengths, areas and angles.

### Square Areas

Can you work out the area of the inner square and give an explanation of how you did it?

# Blue and White

##### Stage: 3 Challenge Level:

We received correct solutions (that the areas were all the same) from:

• Charles Blackham (Shrewsbury House School)
• Michael Brooker (home educated),
• Andrei Lazanu (School number 205, Bucharest),
• Chong Ching Tong, Chen Wei Jian and Teo Seow Tian (River Valley High School, Singapore) and
With one circle in the square the diameter is the length of one side of the square. The shaded area is ${\pi}{r^2}$ where $r$ = radius of the largest circle.
With four circles in the square, the diameter of one circle is half that of the large circle. The area of each small circle is ${\pi}({r/2}\: \times \:{r/2})$. The total shaded area is $4({\pi}{r^2}/4)$. This can be simplified to ${\pi}{r^2}$. \par With nine circles in the square, the diameter of one circle is a third that of the large circle. The area of each small circle is $\pi(r/3\: \times\: r/3)$. The total shaded area is $9({\pi}{r^2}/9)$. This can be simplified to ${\pi}{r^2}$.
We can go one step further by saying that with $n$ circles the area is $n({\pi}{r^2}/n)$ - which can again be simplified to ${\pi}{r^2}$. Therefore the answer is that the shaded area is the same in each picture.