You can upgrade lighting at your factory to led bulbs that cost $6.95 each and last an average of 5 years. it costs $3 in labor to change a bulb. over a 10-year period, about how much will it cost per year to install led bulbs in 100 lamps and change the bulbs when they burn out?

Each bulb and the labor to install it costs
.. $6.95 +$3 = $9.95

100 bulbs and 10 years totals (100*10) = 1000 bulb·years. For the price of $9.95, you purchase 5 bulb·years, so the total cost for 1000 bulb·years is
.. (1000 b·y)*($9.95/(5 b·y)) = $1990

Over a 10-year period, installation and replacement of 200 bulbs in 100 lamps will cost $1990. Then the per-year cost is ...
.. $1990/(10 yr) = $199/yr

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