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#### karush

##### Well-known member

- Jan 31, 2012

- 2,813

a disc is selected at random and its color noted.

The disc is then replaced in the box.

a) In 8 such selections what is the probability that a black disk is selected.

i) exactly once ii) at least once

b) The process of selecting and replacing is carried out 400 times

what is the expected number of black discs that would be drawn.

well there are 40 discs so the probability of selecting a black disk it 1 to 8 so i would presume "at least once" is 8 times. but not sure about the "exactly once"

about 400 times, not sure how this is done I just 400/8 to get 50

I don't know the answers to these so just see what would be suggested here.