Puzzle 1
Here we have a rectangular room, measuring 30 feet by 12 feet, and 12 feet high.
There is a spider in the middle of one of the end walls, 1 foot from the ceiling (A).
There is a fly in the middle of the opposite wall, 1 foot from the floor (B).
What is the shortest distance that the spider must crawl in order to reach the fly?
The Spider and the Fly, The Canterbury Puzzles, Henry Ernest Dudeney.
workings
hint
answer
print
www.brainbashers.com
/puzzle/zwql
share
Hint
Going down and across the floor isn't the only route.
Answer
40 feet.
Explanation Diagram
If you imagine the room to be a cardboard box, you can 'unfold' the room in various ways, and each route gives a different answer.
We can use Pythagoras' theorem (a2 + b2 = c2 ) to calculate the distances:
distance2 = horizontal2 + vertical2
distance = √(horizontal2 + vertical2 )
Route #1
distance = 1 + 30 + 11 = 42 feet.
Route #2
horizontal = 6 + 30 + 6 = 42 feet.
vertical = 10 feet.
distance = √(422 + 102 ) ≈ 43.174 feet.
Route #3
horizontal = 1 + 30 + 6 = 37 feet.
vertical = 6 + 11 = 17 feet.
distance = √(372 + 172 ) ≈ 43.178 feet.
Route #4
horizontal = 1 + 30 + 1 = 32 feet.
vertical = 6 + 12 + 6 = 24 feet.
distance = √(322 + 242 ) = 40 feet.
Puzzle 3
Using a tap, a nine gallon container and a four gallon container …
… can you measure exactly 6 gallons?
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
www.brainbashers.com
/puzzle/zvom
share
Hint
Start by filling the 9 gallon container, and then use that to fill the 4 gallon container.
Answer
Here are the contents of the containers after each stage:
A B
9 0 fill A
5 4 fill B from A
5 0 empty B
1 4 fill B from A
1 0 empty B
0 1 fill B from A
9 1 fill A
6 4 fill B from A
6 0 empty B
This leaves 6 gallons in container A.
Puzzle 4
Which is larger:
fathoms in a kilometre
hours in a month
Puzzle Copyright © Kevin Stone
workings
hint
answer
print
www.brainbashers.com
/puzzle/zbzl
share
Answer
Hours in a month.
Reasoning
A fathom is 6 feet, which is 1.8288 metres.
So there are 1000 ÷ 1.8288 ≈ 546.8 fathoms in a kilometre.
The shortest month has 28 x 24 hours = 672.
So even the shortest month has more hours than there are fathoms in a kilometre.
next >