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# S1 ND watch

1. How do you know when it is a positive and negative z value for part c. Is it something to do with the bell graph? Could someone please explain this, thanks.

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2. (Original post by Jimmy20002012)
How do you know when it is a positive and negative z value for part c. Is it something to do with the bell graph? Could someone please explain this, thanks.

Posted from TSR Mobile
You're right, it is something to do with the bell graph

If you sketch it and look at what values you need it'll give you an idea of whether z is negative or positive.

If 1% of the values have to be less than 5m (or if you like, 99% of the values are greater than 5m), where will the 5m point be on the graph?

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