- Forums
###### Maths help

Watch

4 months ago

A bag contains 3 green and 5 blue marbles. If Lily picks the marbles and replace them, what is the expected number of times she picks a marble until she gets a blue marble for the second time?

May I have a tip how to start the question? like what kind of equation/distribution am I using there?

May I have a tip how to start the question? like what kind of equation/distribution am I using there?

Original post by Bookworm524

A bag contains 3 green and 5 blue marbles. If Lily picks the marbles and replace them, what is the expected number of times she picks a marble until she gets a blue marble for the second time?

May I have a tip how to start the question? like what kind of equation/distribution am I using there?

May I have a tip how to start the question? like what kind of equation/distribution am I using there?

This is the second question you have posted tonight ... you need to post what you've tried as per forum rules.

Original post by Bookworm524

A bag contains 3 green and 5 blue marbles. If Lily picks the marbles and replace them, what is the expected number of times she picks a marble until she gets a blue marble for the second time?

May I have a tip how to start the question? like what kind of equation/distribution am I using there?

May I have a tip how to start the question? like what kind of equation/distribution am I using there?

Its similar to a geometrical distribution as you keep going until you have a "success". Youre asked for the expected value which is the usual sum over x_i * p_i. So if you keep going until youve picked two blue marbles in each case, what are the p_i's? Drawing it as a "ragged" tree may help you think about the different possiblities.

(edited 4 months ago)

- TSR Study Together - STEM vs Humanities!
- How important is maths in a-level physics?
- Help Studing GCSE'S
- Should I take A level Further Math?
- Further maths and maths A level help
- A-level choices
- I need help for my higher tier gcse math resit
- Further Maths/Maths tutoring
- What is the syllabus for the futher maths gcse this year?
- Does further maths help with maths entrance exams?
- Pharmacy degree
- maths help
- GCSE Preparation and Online Resources for it.
- 4 A-levels?
- Which a levels to pick? Any suggestions
- Maths Help Plz
- How to improve GCSE Math grade within these few months
- EPQ or AS maths? Help!!
- could i go from a grade 2 to a grade 5 in Maths
- A Level Maths tuition

- lnat results thread 2024
- Last Person To Post Here Wins (Part 54)
- Law offers - 2024 entry
- Girls Vs. Boys (Part 46)
- Oxford MSc in Digital Scholarship 2024
- World cuisines hurt/heal game
- Official Oxford 2024 Postgraduate Applicants Thread
- Culture, Media and Creative Industries BA in KCL
- HKU / CUHK Medicine non-jupas 2024
- MSc Global Governance and Diplomacy at Oxford - 2024/2025
- HKU BDS 2024 Dentistry
- Lucy Cavendish college 2024
- Mst in English (all streams)
- MPhil Environmental Policy
- Good cheap private exam centres?
- my study diary - gyg ‘24
- Official Imperial College 2024 Undergraduate Applicants Thread
- Cambridge Mathematics Part III Applicants 2024
- Best MSc for a top PhD program
- TSR opinion poll, Feb 2024: how would you vote in the general election?

- Do sixth forms have cheerleaders and sport competitions?
- NHS trust says transgender milk just as good for babies as normal milk
- Official London School of Economics and Political Science 2024 Applicant Thread
- University of Liverpool A100 2024 Entry Applicants
- Official York St John University Applicant Thread for 2024
- Boardworks A-level Biology
- Advice needed
- Official: University of Bristol A100 2024 Entry Applicants
- The Fast Food Restaurants Hurt/Heal game
- Official: Imperial College London A100 2024 Entry Applicants
- English County Hurt / Heal Game
- The NYT games hurt/heal game
- The Russell Group hurt/heal game (Part 5)
- Hurt or Heal (Actors edition)
- Medicine with GCSE combined science
- Supermarket Hurt/Heal Game
- CTAM: Count to a million (Part 79)
- The G20 Leaders Hurt/Heal Game
- The Cambridge College Hurt/Heal Game [part 2]
- The Forum Games Hurt/Heal Game

- Mock set 4 paper 2 q14 a level maths (4 distinct points)
- UKMT Intermediate Math Challenge 2024 - Discussion
- Help with complex summation further maths a levels
- GCSE Mathematics Study Group 2023-2024
- Could I have some help with this suvat question?
- MAT practice
- A-level Mathematics Study Group 2023-2024
- Alevel Maths Question
- weird cosine question
- Series function not differentiable at a point

- hyperbolic function catenary problem
- can anyone answer this A level vectors question (very challenging)
- STEP foundation module help pls
- Ukmt IMC 2024
- ukmt imc
- This maths question is driving me crazy
- Maths Mechanics
- Confused on surds question
- HNC MATHS A2 Task 3 (Radio Transmitters)
- Senior Maths Challenge 2023

- Mock set 4 paper 2 q14 a level maths (4 distinct points)
- UKMT Intermediate Math Challenge 2024 - Discussion
- Help with complex summation further maths a levels
- GCSE Mathematics Study Group 2023-2024
- Could I have some help with this suvat question?
- MAT practice
- A-level Mathematics Study Group 2023-2024
- Alevel Maths Question
- weird cosine question
- Series function not differentiable at a point

- hyperbolic function catenary problem
- can anyone answer this A level vectors question (very challenging)
- STEP foundation module help pls
- Ukmt IMC 2024
- ukmt imc
- This maths question is driving me crazy
- Maths Mechanics
- Confused on surds question
- HNC MATHS A2 Task 3 (Radio Transmitters)
- Senior Maths Challenge 2023

The Student Room and The Uni Guide are both part of The Student Room Group.

© Copyright The Student Room 2024 all rights reserved

The Student Room and The Uni Guide are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: Imperial House, 2nd Floor, 40-42 Queens Road, Brighton, East Sussex, BN1 3XB