Algebra: Proportions

Question

The energy 𝑊 used by a device is directly related to the current 𝐼, the voltage 𝑉, and the length of time 𝑡, for which the energy is used. If a 240-V clothes drier draws a current of 15 A and in 45 min uses 2.7 kWh (kilowatt hours) of energy, how much energy will a 120-V light bulb use, which draws a current of 1.25 in 8 h of use

Answer 1

ok there are same type of info with different numbers for both cases.

so if we focus on the changes in the ratios of each data:

120V / 240V = 1 / 2

1.25A / 15A = 1 / 12

8hr / 45min = 8 * 60 / 45 = 32 / 3

so the product of the change ratios for each value times the first energy value gives us the value for the second example:

(1 / 2) * (1 / 12) * (32 / 3) * 2.7kWh = 1.2 kWh