An alternative to CFL bulbs and incandescent bulbs are light-emitting diode (LED) bulbs. A 60 W incandescent bulb can be replaced by a 12 W LED bulb. Both produce 800 lumens of light. Assuming the cost of electricity is $0.29 per kilowatt-hour, how much does it cost (in dollars) to run the LED bulb for one year if it runs for six hours a day?

Cost = $ 7.62

Explanation:

First we find the energy consumed by the LED bulb during one year, for six hours a day runtime:

E = Pt

where,

E = Energy Consumed = ?

P = Power = (12 W)(1 KW/ 1000 W) = 0.012 KW

t = time of use = (1 year)(365 days/ 1 year)(6 h/ 1 day) = 2190 h

Therefore,

E = (0.012 KW)(2190 h)

E = 26.28 KWh

Now, we find the cost of running LED:

Cost = (E)(Unit Price)

Cost = (26.28 KWh)($ 0.29/ KWh)

Cost = $ 7.62

multiply 2kg by latent heat of vap

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form