View Full Version : Coin tossing problem

01-16-2005, 12:28 PM
Wouldn't mind a little help with this one. Got a test tomorrow and I don't really know how to do questions of this ilk. I have past papers but no answers /images/graemlins/frown.gif

Here it is :

The probability of obtaining a head when a certain coin is tossed is 0.4. The coin is tossed 10 times.

Find the probability that there are exactly 3 heads and the third head occurs on the tenth toss.

I can do the exactly 3 heads part, just not sure how to take into account the last coin being a head? Thanks.

01-16-2005, 01:01 PM
Just split the question into two parts:
1. Probability of getting 2 heads in 9 tosses
2. Probability of getting a head in a single toss (last toss)

P(1) x P(2) = P(event)

01-16-2005, 01:13 PM
Ah, as easy as that? Cute. Thanks /images/graemlins/smile.gif