Year 12s: what will be the first way you research your future options? >>

Normal distribution

Could somebody possibly check over this for me? I thought my method was correct but it's the first question on a past paper and they normally give 'nicer' values for the answer (not sure how to phrase that sorry!) which specifically appear in the tables so now I'm doubting it.

Question:
Y is normally distributed with mean

\mu

and standard deviation 2.50. Given that

P(Y>12) = 0.3

find the value of

\mu

.

I've done:

P(Z < \frac{12 - \mu}{2.5}) = 0.7

From the normal tables,

\frac{12 - \mu}{2.5} = 0.52433?

Rearrange to get

\mu = 10.7

to 3sf.

Thank you!

Reply 1

DylanJ42

Original post by olivia30

looks good to me :biggrin:

are you edexcel for maths?

Reply 2

Zacken

Original post by olivia30

...

What normal tables are you using? I haven't seen ones in the formula booklet with that much accuracy, are you on OCR or something? :eek:

Reply 3

olivia30

Original post by Zacken

What normal tables are you using? I haven't seen ones in the formula booklet with that much accuracy, are you on OCR or something? :eek:

Original post by DylanJ42

looks good to me :biggrin:

are you edexcel for maths?

Thanks both of you! I'm OCR. My tables gave me p(0.524)=0.6999 so I used linear interpolation (is that what it's called) to get the .33 on the end. Not really necessary since they only ask for answers to 3sf but oh well :h: