Is this the right method? Watch

ThisIsAbsolution
Badges: 0
#1
Report Thread starter 8 years ago
#1
I couldn't find a mark scheme for May 2006 OCR S1 so ill check on here.

The random variable Z has the distribution B-(n,0.27), find the smallest value of n such that P(Z \geq 1) > 0.95

This is work so far

P(Z \geq 1) > 0.95 = 1 - P(X = 0) > 0.95

Therefore, P(Z = 0) < 0.05

^n\mathrm{C}_0 \times 0.27^0 \times 0.73^n &lt; 0.05

So, 0.73^n < 0.05

n(Log0.73) < log0.05)

n > log0.05/log0.73

n > 9.51

n = 10

Im sure that for 3 marks this is way too much, if theres a simpler/correct method that would be much appreciated :p:
0
reply
nuodai
Badges: 14
#2
Report 8 years ago
#2
Apart from writing X when you should have written Z, and writing log(0.73)/log(0.05) instead of log(0.05)/log(0.73) [although it seems you calculated the latter], that seems right to me. You might be able to use tables to get to the answer, which could be why it's only worth 3 marks, but I'm not 100% sure about that.
reply
ThisIsAbsolution
Badges: 0
#3
Report Thread starter 8 years ago
#3
(Original post by nuodai)
Apart from writing X when you should have written Z, and writing log(0.73)/log(0.05) instead of log(0.05)/log(0.73) [although it seems you calculated the latter], that seems right to me. You might be able to use tables to get to the answer, which could be why it's only worth 3 marks, but I'm not 100% sure about that.
ah there we go, i was copying out of my book so i must have missed it out..cheers for that

thats what i thought, but the Probability only seems to go up in steps of 0.05 in my books after it goes from 0.1, like 0.15, 0.2, 0.25, 0.3

Fair enough, i was a bit confused when i had to bring in logs to solve a question that is halfway through the Statistics paper..
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of East Anglia
    All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
    Wed, 30 Jan '19
  • Aston University
    Postgraduate Open Day Postgraduate
    Wed, 30 Jan '19
  • Solent University
    Careers in maritime Undergraduate
    Sat, 2 Feb '19

Brexit: Given the chance now, would you vote leave or remain?

Remain (1119)
78.91%
Leave (299)
21.09%

Watched Threads

View All
Latest
My Feed