The amount of time a certain brand of light bulb lasts is normally distribued with a mean of 1500 hours and a standard deviation of 90 hours. Out of 165 freshly installed light bulbs in a new large building, how many would be expected to last more than 1640 hours, to the nearest whole number?

pretty sure 750 each month!

step-by-step explanation:

geometry: triangles

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call the larger triangle abc

then the smaller triangle cde is similar to abc (all angles are equal, aaa).  

ab is the side that is 36, and we wish to find de, the side corresponding to ab

area_cde = area_abc - area_cde --> area_abc / area_cde = 2

let x=length of de

ratio of areas = (ratio of sides)^2

+2+=+%2836%2fx%29%5e2+

+2+=+1296%2fx%5e2+

++x%5e2+=+1296%2f2+=+648+

25.45584

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step-by-step explanation: