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Financial Maths - Household expenses.
Test Yourself 1.


Electricity. 1. Daria received two quotations for the supply and installation of an energy system in her home. They were $6,750 and $7,000.

By what percentage (to the nearest %) does the more expensive quote exceed the cheaper price?

Answer.The second quote is higher than the first by 11%.

2. An average laptop computer draws about 250 watts per hour.

(i) If a laptop is turned on for an average of 12 hours per day, how many kilowatt hours of electricity does it draw?

(ii) If electricity costs are $0.289 /kwh, how much does if cost to run a computer for 12 hours per day for 1 year (365 days) with the computer turned off for the remaining 12 hours?

(iii) If a laptop always remains plugged in and never turned off, how much does it cost per year in electricity charges?

(iii) A laptop on standby draws power at the rate of about 6 W per hour. If instead of leaving the computer on power for 12 hours per day, it is used for 8 hours with the remaining 4 hours on standby (and turned off for 12 hours) what costs savings are achieved?


  3. Richard is considering purchasing a new refrigerator and has narrowed down his choice to two options:

Electrolux: 3 star energy rating of 394 kWh/year
Kevinator: 4½ star energy rating of 310 kWh/year

How much would Richard save in electricity in one year by purchasing the more efficient refrigerator? Assume that electricity charges will remain constant at 28.9 c/kWh.


4. The average household daily electrical use in Australia is 19.2 kWh.

The average residential utility rate is 13c per kWh.
In Sydney, a leading energy company charges 28.9c per kWh.

Over a 90 day period, how much more would an average household pay for their electricity in Sydney compared to the average Australian cost?


Water. 7.
Gas. 11.