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More details are on the attached graph.
the height of the poster must be multiplied by the ratio which is 1 to 2.5 which is 40 cm.
The probability is 0.9671.
The z-score for this is given by
z = (x - μ)/(σ/√n)
z = (38000-37500)/(1561/(√33)) = 1.84.
Using a z-table (http://www.z-table.com) we see that the area under the curve to the left of, less than, this is 0.9671.
7 - 8 = -1
the rate of change is -1
Hope this is right,
Batgirl12