If there are 10 crayons in a bag with 4 green, 4 red and 2 blue you have :
4 chances out of 10 to get a green crayon, 4 chances out of 10 to get a red crayon and 2 chances out of 10 to get a blue one.
On the first try, you have 4 chances out of 10 to get a red crayon.
If you take this crayon out of the bag, it means that there are 9 crayons remaining with just three red crayon.
Then, you have 3 out of 9 chances to get a red crayon on the second try.
In order to know the probability to get a red crayon each try, we have to multiply each probability :
4/10 * 3/9 = 2/90
12/90 = 2/15
So you have 2 chance out of 15 to get 2 red crayons in a row
