question: given a test with mean of 73 and standard deviation of 12.... (continued)

israel1machorro

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given a test with mean of 73 and standard deviation of 12:

i) find the probability a result is between 74 and 80.
ii) find the probability result is less than 60.
iii) find the probability a result is more than 90.
iv) find the score that Is larger that 30% of the result.
v) find the scores that on either side of the middle 20% of results.

so what I know is that standard deviation is the (square root: (x - the mean)2 /N-1) however bringing the probability up is the part I am confused on. what type of probability? and i am corporating it to like say between certain numbers 74 and 80.I am new to this so I have no idea sorry lol. there practice problems for me.
 
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Try converting your two raw scores in to z-score using the formula. Once you have those two answers use the z-table to give you your final answer. For an example: Find the probability that a normal random variable X with mean of 25 and a standard deviation of 5 lies between 15 and 25.
Z=(x-mean)/standard deviation. So for my example 15-25=-10/5 which equals -2. 25-25=0/5 which equals 0. I would then go to the z-table. Now I have 0.5000-0.0228=0.4772. I hope this helps!
 
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