Puzzle 29
Complete the fifth circle with the correct dots.
Puzzle Copyright © Kevin Stone
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Hint
At each stage, a new dot appears at the top.
Answer
Reasoning
At each stage, a new dot starts at the top. The first dot moves clockwise, the second dot moves counter-clockwise, the third dot moves clockwise, etc.
Puzzle 30
Three teachers were discussing how long they had been teaching.
Alex and Billie had been teaching for a total of 36 years.
Charlie and Billie had been teaching for a total of 22 years.
Charlie and Alex had been teaching for a total of 28 years.
How long had each been teaching?
Puzzle Copyright © Kevin Stone
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Hint
If we look at all of the clues, each person appears exactly twice.
Answer
Alex had been teaching for 21 years.
Billie had been teaching for 15 years.
Charlie had been teaching for 7 years.
Reasoning
If we look at all of the clues, each person appears exactly twice.
So the total of the three clues gives us two lots of Alex + Billie + Charlie = 36 + 22 + 28 = 86.
So, Alex + Billie + Charlie = 43 years.
In each clue we are given two of the people, so we can use this to find the missing person:
Charlie and Billie had been teaching for a total of 22 years, which means that Alex must be: 43 – 22 = 21 years.
Charlie and Alex had been teaching for a total of 28 years, which means that Billie must be: 43 – 28 = 15 years.
Alex and Billie had been teaching for a total of 36 years, which means that Charlie must be: 43 – 36 = 7 years.
Reasoning With Algebra
Let Alex = A, Billie = B and Charlie = C, then:
[1] A + B = 36
[2] C + B = 22
[3] C + A = 28
If we use [3] – [2] we have:
[4] A – B = 6
If we use [1] + [4] we have:
2A = 42
A = 21
By [1] B = 15. By [3] C = 7.
Puzzle 31
Which of the shapes is identical to the first one?
There might be more than one.
Puzzle Copyright © Robert A. Hartmann
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Hint
Try to rotate them around in your head, but watch out for mirror images.
Puzzle 32
What day would tomorrow be if...
...yesterday was five days before the day after Sunday's tomorrow?
Puzzle Copyright © Kevin Stone
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Hint
Try working backwards.
Answer
Saturday.
Reasoning
It's best to work backwards:
"Sunday's tomorrow"
is Monday.
"the day after Sunday's tomorrow"
is therefore Tuesday.
"five days before the day after Sunday's tomorrow"
is therefore Thursday.
"yesterday was five days before the day after Sunday's tomorrow"
yesterday was Thursday, making today Friday. Therefore tomorrow is Saturday.
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