Puzzle 18
What is the 10th prime number?
2, 3, 5, 7, …
workings
hint
answer
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Hint
The first nine prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23.
Answer
29.
The first ten prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29.
Puzzle 19
Can you find three words …
… which contain two consecutive i's.
workings
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answer
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Hint
The words begin with the letters R, S, T.
Answer
RADII, SKIING, TAXIING.
You could also have GENII.
Puzzle 20
How many squares, of any size, are on a board divided up into 6 squares by 6 squares?
workings
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Hint
How many 1 x 1 squares are there?
Answer
91 squares.
Reasoning
Squares of size:
1 x 1 = 36
2 x 2 = 25
3 x 3 = 16
4 x 4 = 9
5 x 5 = 4
6 x 6 = 1
Total = 36 + 25 + 16 + 9 + 4 + 1 = 91.
