# Stats helpWatch

#1
Could anyone do this stats question on Normal Distribution and tell me what they got for mean and SD? I've done it but my answers seem really off. Thanks in advance.

Assume that the lifetime of a certain type of light bulb can be modelled by the Normal
distribution. It is found that 6% of bulbs last for more than 1100 hours and 14% for less
than 970 hours.
What is the mean lifetime of a light bulb?
What is the standard deviation of the lifetime of a light bulb?
0
1 week ago
#2
(Original post by SS__)
Could anyone do this stats question on Normal Distribution and tell me what they got for mean and SD? I've done it but my answers seem really off. Thanks in advance.

Assume that the lifetime of a certain type of light bulb can be modelled by the Normal
distribution. It is found that 6% of bulbs last for more than 1100 hours and 14% for less
than 970 hours.
What is the mean lifetime of a light bulb?
What is the standard deviation of the lifetime of a light bulb?
0
1 week ago
#3
I got the mean to be 1023.296607 and the standard deviation as 49.33412423
0
1 week ago
#4
µ = 1023, σ = 49.3
1
#5
(Original post by Notnek)
Ah probz shoulda done that....my bad. The others got the same answer so it’s fine I guess.
0
#6
(Original post by the bear)
µ = 1023, σ = 49.3
Thank you, ended with that too
0
1 week ago
#7
(Original post by SS__)
Thank you, ended with that too
i got it from here:

the first answers look much better than the second ones
0
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