Puzzle 1
Alex and Billie have to empty all of the bookshelves in the library, and move the books into storage.
Alex, on her own, can empty the bookshelves in 18 hours.
Billie, on her own, can also empty the bookshelves in 18 hours.
Unfortunately, Drew likes to move the books from storage back onto the bookshelves, and she can refill the bookshelves in 36 hours.
How long will it take the three of them, working at the same time, to empty the bookshelves?
Puzzle Copyright © Kevin Stone
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Hint
How many rooms can Alex clear in 36 hours?
Answer
12 hours.
Reasoning
In 36 hours, Alex could empty 2 lots of bookshelves, Billie could also empty 2 lots of bookshelves, and Drew could refill 1 lot of bookshelves.
So, 2 + 2 − 1 = 3 lots of bookshelves in 36 hours. Which is 12 hours for one lot of bookshelves.
Alternative Reasoning
Alex and Billie can each empty 1 /18 of the bookshelves in 1 hour, but Drew will refill 1 /36 of the bookshelves in one hour.
So in one hour we have 1 /18 + 1 /18 − 1 /36 = 1 /12 .
So it would take 12 hours to empty the bookshelves.
Puzzle 2
What are the next three digits in this sequence:
7 · 3 · 1 · 8 · 2 · 8 · 5 · 3 · 1 · 5 · 3 · 0 · 3 · 3 · 1 · 4 · 3 · 0 · ? · ? · ?
Puzzle Copyright © Kevin Stone
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Hint
This question involves the months of the year in some way.
Answer
4 3 1.
Reasoning
This is the sequence of the length of the name of the month, and the number of days in that month.
7 3 1 = January, which has 7 letters, and 31 days.
8 2 8 = February, which has 8 letters, and 28 days.
5 3 1 = March, which has 5 letters, and 31 days.
5 3 0 = April, which has 5 letters, and 30 days.
3 3 1 = May, which has 3 letters, and 31 days.
4 3 0 = June, which has 4 letters, and 30 days.
Which means the next three digits are:
4 3 1 = July, which has 4 letters, and 31 days.
Puzzle 3
Starting in the bottom left corner and moving either up or right, how many ways are there to get to the top right corner and make a total of 10?
Note: this puzzle is not interactive, and the numbers cannot be clicked.
Puzzle Copyright © Kevin Stone
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Hint
You can only go up, or right.
Answer
6.
With U = Up, and R = Right, you can move in the following ways:
UURR
URUR
URRU
RUUR
RURU
RRUU
Puzzle 4
Which is larger:
seconds in a week
feet in 100 miles
Puzzle Copyright © Kevin Stone
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Hint
There are three feet in a yard, and 1,760 yards in a mile.
Answer
Seconds in a week.
Reasoning
There are 60 x 60 x 24 x 7 = 604,800 seconds in a week.
There are 3 x 1760 x 100 = 528,000 feet in 100 miles.
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