I've really discovered the satisfaction of casual brainteasers this holiday.
Have a go at this one - it requires only high-school level maths, but has a nasty twist to it that necessitates careful thought.
I can give you hints if you want.
>>7747990
>exactly 3 times smaller
>doesn't even specify wether it references area, diameter or radius
>>7747993
>>doesn't even specify wether it references area, diameter or radius
Are you high?
>>7747994
I wish I would, atleast that would give me an excuse
the second I hit send I noticed what a fucking brainfart this was
brb commiting sudoku
3+1=4
>>7747993
>has a diameter exactly 3 times smaller
>doesn't even specify wether it references area, diameter or radius
k
4
>>7747993
Uh. Yes it does.
>"...a diameter exactly 3 times smaller than that of Coin B"
perhaps English isnt your first language, so ill elaborate.
It means:
>"The diameter of coin A is exactly one third of the diameter of coin B"
>>7747996
don't commit sudoku, its extra hard in todays newspaper
>>7747990
4 times. 3 from needing to roll to traverse the bigger circle, 1 from traveling around the circle.
>>7747990
3 times?
>>7747990
It's just 3 times. Radius is just pi*diameter.
3 times, circumferences scale linearly with c=2pi*d so the circumference of B will be a three times of that of A
Big coin is stationary, so its 2(3)pi
small coin turns x number of times, so we can consider it 2(1)piX
6pi=2piX
3=X
>>7747990
coin A revolves 3 times about its own center, and 1 time about coin B's center.
>>7748026
The answer is 4. Three rotations of its own, plus one around the axis of the central coin.
>>7747990
Give us the answer then, OP
Hm, did not consider the fact that the rotation around B counts.
>>7748043
4
as many above me have said. But none of those explanations are intuitive IMO - let me try to explain it for the layman. This is how I did it, because i did not have the intelligence of the above posters who figured it out properly.
Imagine if coin B was infinitely small - it was a single point. Its diameter would be zero. According to the maths, the number of rotations A goes through should be 0, but if you imagine a coin rotating around a point it clearly would revolve once.
If you do a practical experiment with two of the samesize coins you have lying around you would expect the answer to be 1 rotation, but it is 2.
if when you expect 0 you get 1, and when you expect 1 you get 2, it follows that when you expect 3 you get 4.
The answer is 4. In case you are curious I spent about 40 minutes on this one because I am dumb.
>>7747990
one and a half?
>>7748050
Alternatively, you can just consider the motion of the smaller coin's center.
If you let the radius of the small coin be .5 and the radius of the large coin be 1.5, you know the coin's center must travel around a circle with a radius of 2.
>>7747990
1. It rotates three times, but only one revolution. Earth doesn't do 365 revolutions a year.
>>7748081
It rotates 4 times and does 1 revolution.
>>7747997
this
>>7747990
this is that "sat" question that nobody answered correctly
if the perspective is static and you are interested in whether the "A" is oriented legibly, the answer is 4.
but the original question specifies the diameter, so you can assume it is looking for an answer related to it's circumference, which is 3.
The answer is four and pic related should take away any doubt.
>>7748204
nope.
Define the problem more precisely or don't try to prove it.
Do you count to rotations of A around its center? Around B's center? Around something else?
>>7748204
I did this wrong at first by seeing how many circumferences of coin A fit along the edge of coin B. This would mean that the center of coin A is moving along the edge of coin B. If you position them so the coins edges are touching, the center of coin A has to travel 4r.
>>7748227
The reference system is the one of the greater circumference which doesn't move. Once the little circle returned in its position at the top, a point on it has made 4 rotations around its centre.
>>7748227
This.
"How many revolutions..."
Our galaxy spins around a bunch but we don't say that the earth undergoes more revolutions because of it. You assume it is relative to itself. 3 is the answer without specification.
