Question 1052345
z=(x-mean)/sd
=(3500-7100)/2450=-3500/2450=-1.43
probability x<3500 is probability z<-1.43, which is 0.0764.
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For b, I get the same thing.  I am not clear how this is different.
I am not certain what they mean by c.
If it is the probability that all 3 tests are <3500, it would be 0.0764^3, assuming independence, and that is 0.0004.

If it is the probability it happens at least once, then it is 1- probability it doesn't happen three times in a row, which is (1)-(0.9236)^3= 1-(0.7874)=0.2126.