Seven Toss

Hi Laura, long time no see.

1 in won too ate?

Each toss is 50-50 so a single toss is 1 in 2
2nd toss 1 in 4 3rd toss 1 in 8 4th toss 1 in 16
5th toss 1 in 32 6th toss 1in 64 7th toss 1 in 128

Hi Laura

Hi Adrian, yeah long time no see.
Won too ate: correct too.

Carditel: you are correct.

Now I have a sack with 16 red pebbles and 4 white pebbles. What is the probability of getting all 4 white pebbles if you randomly choose 4 pebbles from the sack?

1 in ?

the first one has a probabilty of 4 in 20, the next 3 in 19 and so on.
4/20 * 3/19 * 2/18 * 1/17 = 24/116280
so 1 in 4845.

Exactly what i came up with --- 1 in 4845

Liessa: ok.

I had a math teacher who had too much time in his classe, and he used to make up oodles of these. We'd grown when he said "I have a vase..."
Of course, he'd add more colours, or make us put them back after each pick, or make us predict the average amount of balls in one of the colours... yay...

Amusing story:
One of my father's classmates had a question in his final exams in high school. The question was: "If there are 49 red balls and 1 white ball in a vase, what's the chance of pulling out the white one at random?"
His answer was 50%.
After grading the exams, his teacher asked him "How did you come up with that answer?"
His reply: "It's 50-50. You either have it, or you don't..."