# Rings Question

• May 7th 2011, 10:44 AM
mathbuoy
Rings Question
Please help me with this question. I totally have no idea why the options have decimals(Worried) Thank you (Hi)

http://i.imgur.com/riiYT.png
• May 7th 2011, 12:41 PM
Opalg
Notice that when the chain hangs vertically, the rings are alternately in one of two planes, either in the same plane as the top ring or in a perpendicular plane. If the chain has an odd number of rings in it, then the bottom ring will have a whole number of 180º twists. But if the chain has an even number of rings then the bottom ring must have an additional half-twist.
• May 7th 2011, 07:24 PM
mathbuoy
Thank you explaining!!

Is my reasoning below right?
if it's two rings, the bottom ring makes .5 twist.
if there're 3 rings, the bottom ring makes .5 + .5 twist.
if there're 6 rings, it should be 2.5 twist.

The answer is B(.5, 1.5, 2.5) but i don't understand why it's given as .5, 1.5 and 2.5 and not just 2.5 twist.
• May 8th 2011, 01:27 AM
Opalg
Quote:

Originally Posted by mathbuoy
Thank you explaining!!

Is my reasoning below right?
if it's two rings, the bottom ring makes .5 twist.
if there're 3 rings, the bottom ring makes .5 + .5 twist.
if there're 6 rings, it should be 2.5 twist.

The answer is B(.5, 1.5, 2.5) but i don't understand why it's given as .5, 1.5 and 2.5 and not just 2.5 twist.

The reason is that the twists don't all have to be in the same direction. They can be +.5 or –.5.
• May 9th 2011, 06:22 AM
mathbuoy
But why can't the other answers apply?
• May 9th 2011, 06:31 AM
Opalg
Quote:

Originally Posted by mathbuoy
But why can't the other answers apply?

Because they all include some whole numbers. For an even number of rings, the bottom ring will always have a .5 in its number of twists.