Post by: monokekie on August 06, 2009, 07:09:46 pm
The weight of a packet of biscuits is known to be normally distributed with a mean of 1 kg, if a packet is more than 0.05 kg underweight, it is unacceptable, If it is found that 3 % of packets are unacceptable, then the standard deviation of the weight is?
Post by: zzdfa on August 06, 2009, 07:32:24 pm
if i told you something was 5 standard deviations above the mean, would you know how to find out what % of the population is above that?
this is just the reverse, you're given the % (shaded blue area) and you have to find how many standard deviations from the mean it is (use calculator)
(http://img5.imageshack.us/img5/9072/packet.jpg)
after you do that, you can solve for the standard deviation:
(s is the number of standard deviations away from the mean, if you think about it! and the mean is given, and Z is given as well)
s
Post by: monokekie on August 06, 2009, 07:33:55 pm