# Ch. 6 normal probability distibution

I need help on problem number 20. (a) (b). I need work by tomorrow night 8 pm central time. Please let me know if you can read the attachment.

(1) students are confused by X<=60 inches tall and the % of X<= 60 inches tall (i.e., P(X<=60)) where X=the height, or simply confused z<=1.5 from P(Z<=1.5).

(2) What is the x by given P(X<=x) =0.01, where X is the height? Of course, x is something like 75 inches tall or so depending on the given normal probability distribution. X<=a, X>=b, a<=X<=b and the probabilities for X<=a, X>=b, a<=X<=b, are completely two different things.

(3) Some students got lost at the first moment of using Table 1 on PP. 764-765 to find P(Z<=-0.85) and P(Z<=1.25). Can you find the answers for P(Z<=-0.85)=0.1977 and P(Z<=1.25)=0.8944 from Table 1. If not, please ask yourself what the purple highlight in Table 1 is, and read the fine prints of the explanations on top of the Table. If you still have no clue about them, then it is the time you need to ask for help in Ch. 6 DB. You have to master the use of Table 1 ASAP and no later than Wednesday (basically, you can learn how to find P(Z<=-0.85)=0.1977 and P(Z<=1.25)=0.8944 in about 5 minutes). Once you know how to find P(Z<=-0.85)=0.1977 and P(Z<=1.25)=0.8944, you will be able to find the P(Z>=-0.85)=1-0.1977=0.8023, P(Z>=1.25)=1-0.894=0.1056, and P(-0.85<= Z <= 1.25)=P(Z<=1.25)-P(Z<-0.85)=0.8944-0.1977=0.6967, in no time. Knowing those in about 20 minutes, you have learned 1/4 of the chapter and you will be able to work on Q#8-Q#13. If by the morning of Wednesday, you are still not able to work on Q#18-Q#13, they you have to ask for help, or you may get lost for the rest of this semester.

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