Here is the riddle.
There are 100 cards laying on a table. The front of the cards are red and the back of the cards are black. All of the cards are facing up so they are all red. Someone comes by and turns over all of the cards that are multiples of two, so now the multiples of two are black. Another person comes by and turns all of the multiples of three over. So now the multiples of three are black, and if they were already turned over when they turned over the multiples of two they are changed back to red. This goes on until the person reaches the multiples of one hundred.
In the end, how many of these cards are left with the red side facing up?
What patterns did you find?
Also, how many red cards would be left facing up if you did this with one thousand cards?
Please Help!
Thanks!
There are 100 cards laying on a table. The front of the cards are red and the back of the cards are black. All of the cards are facing up so they are all red. Someone comes by and turns over all of the cards that are multiples of two, so now the multiples of two are black. Another person comes by and turns all of the multiples of three over. So now the multiples of three are black, and if they were already turned over when they turned over the multiples of two they are changed back to red. This goes on until the person reaches the multiples of one hundred.
In the end, how many of these cards are left with the red side facing up?
What patterns did you find?
Also, how many red cards would be left facing up if you did this with one thousand cards?
Please Help!
Thanks!