The weights of rats in a city are normally distributed with a mean of 2.5 pounds and a standard deviation of 0.5 pounds.

about what percent of the rats in the city weigh between 2.0 pounds and 3.0 pounds?

a. 81.5%

b. 68%

c. 47.5%

d. 34%

About 95%  of rats weight is between 2.5+2 *standard deviation=2.5+2*0.5=2.5+1=3.5 and 2.5-1=1.5 (1.5,3.5).
About 68% of rats weight is between (2.5-1*standard deviation, 2.5+1*standard deviation), (2,3).

This means that about 68 percent of rats in the city weigh between 2 pounds and 3 pounds. (solution b)

The probability that all marbles are yellow is
(7/20) (7/20) (7/20) = 343/8000

We are given
x = 2 and 3
u = 2.5
s = 0.5

Getting the z score
z = (2 - 2.5) / 0.5 and (3 - 2.5)/ 0.5
z = -1 and 1
The percentage is 
1 - 0.1557 = 81.5%

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