# Math

posted by Laurie

If a light bulb that burns 3 hours a day lasts for 22.8 years, then how long will a light bulb that burns for 7 hours a day last?

1. Damon

(3/7)(22.8) =

2. Reiny

burnhours of the lightbulb = 3(22.8) = 68.4

time for a bulb that burns 7 hours/day
= 68.4/7 =9.77
or 9.8 years

or
the time is inversely proportional to the rate
T = k/R
22.8 = k/3
k = 3(22.8) = 68.4
T = 67.4/R
= 67.4/7 = appr 9.8

Notice the calculations are the same

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