Answer:
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9514 1404 393
Answer:
13 cm wide; 15 cm long
Step-by-step explanation:
Let w represent the original width. Then the original length is (w+2) and the original area is w(w+2). After the decrease, the width is (w-1) and the length is (w+1). The decreased area is (w-1)(w+1). The difference between these areas is 27, so we have ...
w(w+2) -(w-1)(w+1) = 27
w^2 +2w -(w^2 -1) = 27
2w +1 = 27
w = (27-1)/2 = 13
The original piece of cardboard was 13 cm wide and 15 cm long.
Approximately 65% of the distribution lies within one standard deviation of the mean, which is to say,
P(72 ≤ x ≤ 86) ≈ 0.65
Normal distributions are symmetric, so the percentage of values one standard deviation below the mean is equal to the percentage of values one standard deviation above the mean.
P(72 ≤ x ≤ 79) = P(79 ≤ x ≤ 86)
but since the sum of these make up P(72 ≤ x ≤ 86), we find
P(72 ≤ x ≤ 79) ≈ 0.65/2 = 0.325
Also due to symmetry, exactly half of the distribution lies to either side of the mean; namely,
P(x ≥ 79) = 0.5
It follows that
P(x ≥ 72) = P(72 ≤ x ≤ 79) + P(79 ≤ x)
P(x ≥ 72) = 0.325 + 0.5
P(x ≥ 72) = 0.825 ≈ 0.84
