• Support PF! Buy your school textbooks, materials and every day products Here!

Probability Question

  • Thread starter bjgawp
  • Start date
84
0
1. Homework Statement
On average a certain jockey falls from her horse once in every 10 rides. What is the probability that she will fall from her horse at least once in the next ten rides?


2. Homework Equations
Answer is 0.651.


3. The Attempt at a Solution
I've no idea .. I thought of adding up the probabilities of the jockey falling once, twice, thrice, etc. but that just gives me an answer greater than 1 which would not make sense.

P(Fall at least once) = (1/10) + (1/10 + 1/10) + (1/10 + 1/10 + 1/10) + ...
= 55/10
 

Answers and Replies

cristo
Staff Emeritus
Science Advisor
8,056
72
You want to add up the probability that the jockey falls once out of the ten jumps+ the probability that the jockey falls twice out of the ten +... The probability that the jockey falls once is equal to 0.1*0.9*0.9*...*0.9 (where there are nine 0.9's).

Summing this for all the possibilities (i.e. 1 to 9 falls) will give the answer. However, can you see a quick way of doing this? What must the sum of the probability of all the choices (i.e. falls no times, falls once, falls twice...) be?
 

Related Threads for: Probability Question

  • Last Post
Replies
5
Views
917
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
2
Views
980
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
2
Views
1K
Top