The Student Room Group

S1 Normal Distribution

'The time Y minutes to install a gas meter has a mean of 37 and a standard deviation of 25.

Explain why Y is unlikely to be normally distributed.'

The mark scheme answer is:

'mean - (2 or 3) x standard deviation = 37 - (50 or 75)

<0 --> likely negative times'

Can someone explain the answer please?
Reply 1
Original post by SherlockHolmes
'The time Y minutes to install a gas meter has a mean of 37 and a standard deviation of 25.

Explain why Y is unlikely to be normally distributed.'

The mark scheme answer is:

'mean - (2 or 3) x standard deviation = 37 - (50 or 75)

<0 --> likely negative times'

Can someone explain the answer please?



Hi, I'm not really sure but anyway I think: the standard normal distribution has a mean of 0 and standard deviation of 1 and it's spread across 3 standard deviations either side so 0 to 3 & 0 to -3 now here if the mean is 37 then the standard deviation to the left will go to ( 25 x 3 ) = 75 but because it's to the left it will be -75 & you can't get a time of -75 mins? :confused: Again I'm not sure but that's what I think :s-smilie:
Original post by Fortitude
Hi, I'm not really sure but anyway I think: the standard normal distribution has a mean of 0 and standard deviation of 1 and it's spread across 3 standard deviations either side so 0 to 3 & 0 to -3 now here if the mean is 37 then the standard deviation to the left will go to ( 25 x 3 ) = 75 but because it's to the left it will be -75 & you can't get a time of -75 mins? :confused: Again I'm not sure but that's what I think :s-smilie:


Ah I see - that sounds right. Thanks for the help :smile:
Reply 3
Original post by SherlockHolmes
Ah I see - that sounds right. Thanks for the help :smile:



Your welcome :biggrin:

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