The Student Room Group

GCSE Probability Question..

In a game, players take it in turns to flip two fair coins.
If a player gets 1 head they score 1 point.
If a player gets 2 heads they score 3 points.
The object of the game is to get 7 or more points.
Work out the probability of a player getting 7 or more points on their third turn.

I got 2/64 but I don't have the correct answer. Pretty sure that's probably wrong but could anyone do it and walk through it..?
Original post by Fudge2
In a game, players take it in turns to flip two fair coins.
If a player gets 1 head they score 1 point.
If a player gets 2 heads they score 3 points.
The object of the game is to get 7 or more points.
Work out the probability of a player getting 7 or more points on their third turn.

I got 2/64 but I don't have the correct answer. Pretty sure that's probably wrong but could anyone do it and walk through it..?


I get 847212\dfrac{847}{2^{12}} as probability player A gets 7 or more on their third throw, plus the probability that player A gets less than 7 times the probability that player B gets 7 or more on their third throw.

Consider one player.

Work out the distribution for first attempt,
Then for the second attempts.

Notice that no player can get 7 or more on two throws.

Then work out the distribution for the third attempt.
Note: You're only interested in whether it's >=7 or not, so you don't need to work them all out.

I get:

Spoiler

(edited 9 years ago)
Reply 2
Original post by ghostwalker
I get 847212\dfrac{847}{2^{12}} as probability player A gets 7 or more on their third throw, plus the probability that player A gets less than 7 times the probability that player B gets 7 or more on their third throw.

Consider one player.

Work out the distribution for first attempt,
Then for the second attempts.

Notice that no player can get 7 or more on two throws.

Then work out the distribution for the third attempt.
Note: You're only interested in whether it's >=7 or not, so you don't need to work them all out.

I get:

Spoiler



Thanks for your help :smile:

Quick Reply

Latest