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Normal distribution question? URGENT!!

X-N (45, SIGMA)
P(W<54)=0.75
SO 54-45/SIGMA = 0.67
I don't understand where the 0.67 has come from, it's not in any of the tables :frown: what happened to the 0.75, why is it 0.67
This came up in a paper before but I didn't understand it :'(
This question was from June 2007 Edexcel S1 Q2e
Please help me someone, my exam is tomorrow!
Thanks :smile:
BUMP
Sorry for the bumping but this is really urgent
Original post by Cinnamon_Twist
X-N (45, SIGMA)
P(W<54)=0.75
SO 54-45/SIGMA = 0.67
I don't understand where the 0.67 has come from, it's not in any of the tables :frown: what happened to the 0.75, why is it 0.67
This came up in a paper before but I didn't understand it :'(
This question was from June 2007 Edexcel S1 Q2e
Please help me someone, my exam is tomorrow!
Thanks :smile:


just so I can find it easily
P(W<54)=0.75P(W<54)=0.75


P(Z<5445σ)=0.75P(Z<\frac{54-45}{\sigma})=0.75

Reading backwards from the tables, P(Z<0.67)0.75Reading \ backwards \ from \ the \ tables, \ P(Z<0.67) \approx 0.75

 P(Z<5445σ)P(Z<0.67) i.e. 5445σ0.67\therefore \ P(Z<\frac{54-45}{\sigma}) \approx P(Z<0.67) \ i.e. \ \frac{54-45}{\sigma} \approx 0.67
Reply 5
I think you may be over-complicating things. Doesn't the question just ask you to find σ\sigma? You've done most of the work already!
Original post by Implication
P(W<54)=0.75P(W<54)=0.75


P(Z<5445σ)=0.75P(Z<\frac{54-45}{\sigma})=0.75

Reading backwards from the tables, P(Z<0.67)0.75Reading \ backwards \ from \ the \ tables, \ P(Z<0.67) \approx 0.75

 P(Z<5445σ)P(Z<0.67) i.e. 5445σ0.67\therefore \ P(Z<\frac{54-45}{\sigma}) \approx P(Z<0.67) \ i.e. \ \frac{54-45}{\sigma} \approx 0.67


Thank you so so so so much! +rep

Original post by olipal
I think you may be over-complicating things. Doesn't the question just ask you to find σ\sigma? You've done most of the work already!


yeah, I think I just panicked because the exam is tomorrow- thanks for the reassurance!
+rep
Reply 8
Original post by olipal
I think you may be over-complicating things. Doesn't the question just ask you to find σ\sigma? You've done most of the work already!


Maths, Palmer Maths

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