Your task is to make the top and bottom cogs turn clockwise, as shown by the red arrows in the diagram. In order to do this, which extra cog should be inserted, A, B, or C?
Tap the letter in the center of the correct cog to submit your answer.
Hints
Click a Tab to reveal the Hint.
US Version
To find out how to make both the top and bottom cogs turn in the direction indicated by their respective arrows, try following the cogs from one end to the other, checking each one's direction.
You realize that two adjacent cogs always turn in opposite directions, don't you?
UK Version
To find out how to make both the top and bottom cogs turn in the same direction, try following the cogs from one end to the other, checking the direction of each one.
You do realise that two adjacent cogs always turn in opposite directions, don't you?
US Version
You can find the answer by thinking out the direction of rotation for A, B, and C.
But there's an easier way to find the answer. Try reading Hint One again.
UK Version
With the method explained in Hint 1, you can systematically check the rotation sequence of the cogs when A, B and C are inserted.
However, there is an even quicker way to work out the answer. Try reading Hint 1 again.
US Version
As you know, neighboring cogs move in opposite directions. If three cogs were lined up, the second cog would move in the opposite direction from the first, but the third cog would move in the same direction as the first.
Thinking along those lines, if there's an odd number of cogs between two others, those two cogs will move in the same direction. If the number of cogs between two others is even, those two cogs will move in different directions.
UK Version
As you know from Hint 1, adjacent cogs move in opposite directions. If three cogs were lined up, the second cog would move in the opposite direction to the first, but the third cog would move in the same direction as the first. Thinking along these lines, any two cogs that have an odd number of cogs between will always move in the same direction. Any two cogs with an even number of cogs between them will move in different directions.
US Version
If you insert cog A, there will be four cogs between the top and bottom cogs. If you insert B, there will be five cogs between the two main cogs. Finally, inserting cog C would yield four cogs between the two main cogs, which is the same value as cog A.
UK Version
If you insert cog A, there will be four cogs between the top and bottom cogs.
If you insert cog B, there will be five cogs between the two main cogs.
Finally, inserting cog C would mean there are four cogs between top and bottom, the same as when cog A is inserted.
Solution
Incorrect
Too bad!
US Version
Try using the Memo function to mark the direction in which each cog moves.
UK Version
Try using the Memo Function to mark the direction in which each cog moves.
Correct
Excellent!
The answer is B. If there is an odd number of cogs between the top and bottom cogs, then those two cogs will move in the same direction. However, if there's an even number of cogs between the top and bottom, they will move in opposite directions.
By choosing B, there will be five cogs between the two main cogs, so the direction of their rotation will be the same.