i really need help????????!!!!!!!!!!!!!!?

Question

an energy-efficient lightbulb,taking in 28.0 W of power,can produce the same level of brightness as a conventional bulb operating at a power 100W.the life time of the energy efficient bulb is 10000 h and its purchase price is $17.0,whereas the conventional bulb has life time 750h and costs $0.420 per bulb.

Determine the total savings obtained by using one energy-efficient bulb over its life time,as opposed to using conventional bulbs over the same time of period?
assume an energy cost of $0.0800 per Kilowatt-hour.

Answer 1

Savings = (Cost Conventional) - (Cost Efficient)

(Cost Conventional) = (Energy Cost + Bulb Cost) x Period
(Cost Efficient) = (Energy Cost + Bulb Cost) x Period

Conventional: 100 W * 0.08 $/kWh * 10000 h = 80.00
Over the same period, number of bulbs = 10000/750 = 13.3
So, total cost = 80.00 + (14 * 0.42) = 85.88 (we can't buy a third of a bulb!)

Efficient: 28 W * 0.08 $/kWh * 10000 h = 22.40
Number of bulbs = 10000/10000 = 1
So total cost = 22.40 + (1 * 17.00) = 39.40

Savings = 85.88 - 39.40 = $ 46.48 (over a 10000 hour span).

Answer 2

Bulb 1 Data:
P = 28W
Life time = 10000 hours
Purchase price = $17.0/bulb
Bulb 2 Data:
P = 100W
Lifetime = 750hours
Purchase price = $0.42/bulb

Total energy consumption of bulb1 in kWh = 28*10000 = 280kWh
Energy cost = 280*$0.08 = $22.4
Add to this the cost of the bulb = $17.0, we get
Total expense using bulb 1 = $39.40
Total energy consumption for bulb2 in kWh =100*10000= 1000000 =1000kWh
Energy cost = 1000*$0.08 = $80
add to this the cost of 13 additional bulbs which is obtained by dividing 10000 by 750 = 13 approx.
Total bulbs of type 2 used = 13
their cost = 13*0.42 = $5.46
Total expenditure on bulb 2 = $80 + $5.46 = $85.46
If the energy saving bulb 1 is used then total savings in cost would be;
$85.46 - $39.40 = $46.06

Answer 3

Do the costs for each situation:

energy efficient bulb:

cost of electricity = 28W x 10000 hours x .08 kwh / 1000 = $20.40
Add cost of bulb, total cost = 20.4 + 17


regular bulb:
cost of electricty = 100W x 10000 hours x .08 kwh /1000 = 80
number of bulbs = 10000 / 750 = 13.3, so need 14 bulbs
cost of bulbs = 14 x .42 = 5.90
so total cost = 80 + 5.90

savings = (80 + 5.9) - (20.4 + 17) = 28.50

Answer 4

This problem isn't tough. Just don't let it confuse you.

We can calculate how much each bulb costs per hour of use by adding together the cost of the bulb itself and the cost of the energy that it uses.

The standard bulb costs ($0.42 / 750h lifetime) = $0.00056 dollars per hour of use. Add in ($0.08 per kwh * 0.1kw) = $0.008 dollars per hour for a total of $0.00856 dollars per hour to use the 100W bulb.

The energy-efficient bulb costs ($17.00 / 10000h lifetime) = $0.0017 dollars per hour of use. Add in ($0.08 per kwh * 0.028kw) = $0.00224 dollars per hour for a total of $0.00394 dollars per hour to use the energy efficient bulb.

The question asks how much money is saved over the lifetime of an energy efficient bulb (10,000 hours). We can just multiply our hourly cost by this number to figure out the total cost of operating a bulb for that long.

Standard bulb cost = $0.00856/hr * 10,000 hrs. = $85.60
Energy efficient bulb cost = $0.00394/hr * 10,000 hrs = $39.40

You would save $46.20 (85.60 - 39.40) by using the more expensive bulb.

EDIT:
Sorry, I misplaced a decimal at first.

Also, I disagree that the total cost of 14 bulbs should be included in the calculations. While it's true that you can't buy a third of a bulb, you also can't throw away the remaining value of the bulb. That extra value is still in the bulb and is still usable, thus it is not lost. If it were, we could reframe the question to show that we save money over the lifetime of the standard bulb, because the EE bulb costs so much more initially.

This is probably just a matter of perspective, but that's how I see it.