Download NAME DATE PERIOD ___ Normal Curve Practice 1. Rat weights are

NAME _______________________________________
Normal Curve Practice
DATE _______________
PERIOD ___
1. Rat weights are normally distributed with μ = 6 lbs. and σ = 0.45 lbs., X = N (6, 0.45).
For parts a – e you must use the 68-95-99.7 Rule. Please make a sketch using this rule below.
a. Find the percentage of rats that are less than 6 lbs.
b. Find the percentage of rats that are less than 6.9 lbs.
c. Find the percentage of rats that between 5.1 and 6.9 lbs.
d. Find the percentage of rats that are heavier than 6.45 lbs.
e. Find the percentage of rats that are greater than 8 lbs.
For parts f – g you must calculate the z-scores and use table A.
f. Find the percentage of rats that are less than 7 lbs.
g. Find the percentage of rats that are between 5 and 7 lbs.
Working Backwards
2. Find the value z on the standard normal curve that is less than only the top 25% of the data.
3. Find the value on the curve X = N (15, 3) that is greater than 30% of the population.
4. Find the value in the normal population described in question 3 that would be considered the
95th percentile.
5. Find the boundaries of the middle 90% of the standard normal curve.
6. The distribution of heights of adult American men is approximately normal with mean 69 inches
and standard deviation 2.5 inches. How tall must a man be in the tallest 10% of adult men?
7. Use table A to find the value z of a standard normal variable that satisfies each of the following
conditions. Sketch a standard normal curve with your value of z marked.
a. The point z with 70% of the observations falling below it.
b. Find the number z such that the proportion of observations that are less than z is 0.8.
8. The length of human pregnancies from conception to birth varies according to a distribution that is
approximately normal with mean 266 days and standard deviation 16 days.
a. What percent of pregnancies last less than 240 days (that’s about 8 months)?
b. What percent of pregnancies last between 240 and 270 days (roughly btw. 8 months and 9 months)?
c. How long do the longest 20% of pregnancies last?