The paper “Microwave Observations of Daily Antarctic Sea-Ice Edge Expansion and Contribution Rates” (IEEE Geosci. and Remote Sensing Letters, 2006: 54–58) states that “The distribution of the daily sea-ice advance/retreat from each sensor is similar and is approximately double exponential.” The proposed double exponential distribution has density function for . The standard deviation is given as 40.9 km.

f(x) 5 .5le2l|x| 2` , x , `

l 5 .01386 P(X # 4) P(2 # X # 5)

a 5 1 l 5 1 X 5

a. What is the value of the parameter ?

b. What is the probability that the extent of daily sea-ice change is within 1 standard deviation of the mean value?