Puzzle 117
My friend's son, Billy, has the same number of brothers as sisters.
His sister, Laura, has twice as many brothers as she has sisters.
How many boys and girls are in the family?
Puzzle Copyright © Kevin Stone
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Hint
A little algebra might help.
Answer
There are four boys and three girls.
If we call the number of boys B, and girls G.
From the first statement (we take one off as Billy is a boy):
B − 1 = G
and similarly:
2 x (G − 1) = B
Substitute G from the first equation into the second equation to give:
2 x ((B − 1) − 1) = B
2 x (B − 1) − 2 = B
2 x B − 2 − 2 = B
2 x B − 4 = B
B = 4
which means that B = 4 and hence G = 3.
Puzzle 118
How much soil is there …
… in a circular hole 2 metres deep and 1 metre across?
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Hint
How much soil is in any hole?
Puzzle 119
What belongs to you, but other people use it more than you?
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Puzzle 120
Which is larger:
ounces in gross pounds
seconds in an hour
Puzzle Copyright © Kevin Stone
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Hint
There are 16 ounces in a pound, and 144 in a gross.
Answer
Seconds in an hour.
Reasoning
There are 16 x 144 = 2,304 ounces in gross pounds.
There are 60 x 60 = 3,600 seconds in an hour.
