Riddles, one at a time
Lighthouse Flashes
A lighthouse flashes evenly. From the 1st flash to the 6th takes 5 seconds. How long from the 1st flash to the 11th?
Count the gaps between flashes, not the flashes.
10 seconds
Flash 1 to flash 6 is 5 gaps, so each gap is 1 second. Flash 1 to 11 is 10 gaps.
Stack the Stones
Which number belongs on the top brick?
44
20 - 9 = 11, 13 + 11 = 24, then 24 + 20 = 44.
Split 8 Litres
Fewest pours to share it 4 L and 4 L?
Only the 8 L and 5 L jugs can end with 4 L. Use the 3 L jug as a measure.
7 pours
8→5, 5→3, 3→8, 5→3, 8→5, 5→3, 3→8: 4 L and 4 L.
Three Turning Rings
At which step number are all three gems at the top again?
36 STEPS
Notches 9, 6 and 4: the first common multiple is 36.
Move One Rod
Move exactly one rod. What is the true equation?
9 − 8 = 1
The top rod of the 7 turns the 3 into a 9.
Which Tank Fills?
E
The cap stops A. Water takes each lowest open pipe: B, then D, then E.