# A family replaces 10 60-watt incadescent bulbs with 10 30-watt flourescent lamps. If each light was used for 4 hours a day and the cost of electricity was 10.0 cents/kWh, how much money would they...

A family replaces 10 60-watt incadescent bulbs with 10 30-watt flourescent lamps. If each light was used for 4 hours a day and the cost of electricity was 10.0 cents/kWh, how much money would they save in a year?

how much money would they save in a year?

lemjay | High School Teacher | (Level 2) Senior Educator

Posted on

First, determine the total power of the incandescent bulbs in kW as well as the total power of fluorescent lamps.

For 10 pcs. of 60W incandescent bulb,

`Total Power = 10* 60W = 600W= 0.6kW`

For 10 pcs. of  30W fluorescent,

`Total Power = 10* 30W = 300W = 0.3kW`

Next, determine the power consumption (kWh) of the family in one day. Use the formula:

Total power * number of hours used per day = kWh per day

Note that each bulb is used 4 hours per day.

For 10pcs of 60W incandescent bulb,

`0.6 * 4 = 2.4` kWh per day

And, for 10 pcs of 30W fluorescent bulb,

`0.3* 4 = 1.2` kWh per day

Next, let's determine the power consumption (kWh) per year.

For 10pcs of 60W incandescent bulb,

`2.4 (kWh)/(day)xx (365 days)/(1 year) = 876` kWh per year

And, for 10 pcs of 30W fluorescent bulb,

`1.2(kWh)/(day)xx (365 days)/(1 year) = 438` kWh per year

Then, let's compute the annual electricity cost.

For 10pcs of 60W incandescent bulb,

`876 kWh xx 10 (cents)/ (kWh) = 8760 cents`

And, for 10 pcs of 30W fluorescent bulb,

`438xx 10 (cents)/ (kWh) = 4380 cents`

To solve amount saved, subtract the annual electricity cost of  fluorescent bulb from incandescent bulb.

`8760 - 43820 = 4380`

Hence, the amount saved in electricity cost is 4380 cents.