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The larger circle has diameter = 4, therefore the radius is 2, and the area is π x 2^{2} = 4π.
The smaller circle has diameter = 2, therefore the radius is 1, and the area is π x 1^{2} = π.
Therefore the shaded area is 4π  π = 3π ≈ 9.42.
Circle
The area of a circle is π x Radius^{2}.
The circle with diameter 3.1 has a radius of 1.55 and an area of π x 1.55^{2} = 7.55.
The circle with diameter 3.5 has a radius of 1.75 and an area of π x 1.75^{2} = 9.62 (** closest match).
The circle with diameter 3.9 has a radius of 1.95 and an area of π x 1.95^{2} = 11.95.
Square
The area of a square is Side x Side.
The square with side 3.1 has an area of 3.1 x 3.1 = 9.61 (** closest match).
The square with side 3.5 has an area of 3.5 x 3.5 = 12.25.
The square with side 3.9 has an area of 3.9 x 3.9 = 15.21.
Triangle
The area of a triangle is ½ x Base x Height. Using Pythagoras' theorem it can be shown that the area of an equilateral triangle is Sqrt(3) x Base^{2} ÷ 4.
The triangle with side 3.9 has an area of Sqrt(3) x 3.9 x 3.9 ÷ 4 = 6.59.
The triangle with side 4.3 has an area of Sqrt(3) x 4.3 x 4.3 ÷ 4 = 8.01.
The triangle with side 4.7 has an area of Sqrt(3) x 4.7 x 4.7 ÷ 4 = 9.57 (** closest match).
Puzzle 39
4 shepherds were watching over their flocks and they were commenting on how many sheep they each had.
If Alan had three more sheep, then he'd have one less sheep than Brian.
Whereas Dave has the same number as the other three shepherds put together.
If Charles had three less sheep, he'd have exactly treble the number of Alan.
If they were evenly distributed they'd each have eleven sheep.
If we denote Alan by A, Brian by B, Charles by C and Dave by D we can find the answer in the following way. Since A + B + C = D and A + B + C + D = 44, it is easy to see that D has 22 sheep. So A + B + C = 22. We can use this along with the two other facts, A + 3 = B  1 and C  3 = 3A, to find that A has 3, B has 7, C has 12 and D has 22. In a little more detail:
A + B + C = 22 (1)
A + 3 = B  1 (2)
C  3 = 3A (3)
Rearrange (3) to give C = 3A + 3 and replace the C in (1) to give A + B + 3A + 3 = 22. Simplified this gives B = 19  4A (4). Rearrange (2) to give B  A = 4. Use (4) in the place of B to give 19  4A  A = 4 to give A = 3. Now use A to work out B, and then C.
Puzzle 40
Move from letter to letter and collect the necessary letters for FIND (in any order).
How many different routes can you take if you always start with the central F and always move either horizontally or vertically?
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