I'm not sure how to go about b,c,d here :

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answer = 0.1587

I get (ish) that for part a I can standardise the difference between the desired value and the given mean with

z = [x - \mu] / (\sigma)

(not sure how to render latex...)

And then I can look that up in the Z table, but I'm not sure what to do if i want more than one?

It seems that I have something such as

P(a > 51) :and: P(b > 51) :and: P(c > 51) :and: P(d > 51)

where a,b,c,d are four bags of nuts, but this doesn't seem like a very sensible approach and doesn't give the answer (which is 0.1587)

Cheers