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Optoelectronics, Optics, Lights and Lasers > Non-Coherent Light Sources > Incandescent Lamps > 

easy math word problem please help?

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Author Topic: easy math word problem please help?  (Read 406 times)
hello
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« on: May 28, 2011, 05:51:35 AM »
incandescent light bulb costs $0.75 a bulb and 0.0072 per hour
C= 0.75 + 0.0072 h

fluorescent bulb costs $4 and 0.0018 an hour

C= 4 + 0.0018h

how many hours will it take for the fluorescent to be cheaper?
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Tim_J
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« Reply #1 on: May 28, 2011, 09:13:42 PM »
You need to find the smallest h for which

4 + 0.0018h < 0.75 + 0.0072h

Combine terms...

(0.0072 - 0.0018) h > 4 - 0.75
0.0054h > 3.25
h>601.85

After 601.85 hours, the fluorescent becomes cheaper
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The_Man
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« Reply #2 on: May 29, 2011, 12:02:59 AM »
Graph it!
use c as y1 and y2 then h as "x" find the intercept and put it as greater than intercept!
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