1 i. a. Since z1=0.67 and z2=2.33 then the desired proportion is:
                (98.12-48.43)/2 = 24.845%
     b. Since the z required is the tabled value for 20% and it is 
        -ve then:
                time=(-0.25)60+400=385
     c. The z required for the 95th %tile is the tabled value for
        90%:
                time=(1.65)60+400=499
        Since 508 is greater than 499 then 508 is slower than the 95th 
        %tile.
                
 ii. a. Since s(ybar)=15 then t=(370-400)/15=-2. Since df=16 then the
        desired proportion is between 2.5% and 5%.
     b. FALSE. The sampling distribution for samples of size n=8 is
        "t" but that for samples of size n=64 is normal. The proportions
        are 98% and 99.73%.

2 i. mu=$2.60
 ii. s(ybar)=0.9/sqrt(81)=0.1
iii. The 95% CI is [2.60-(1.95)0.1, 2.60+(1.95)0.1]=[2.405, 2.795] and
     so you are 95% confident that mu is between $2.405 and $2.795.