gl test 6, q 18, help please

[goldenstar]

It takes 324 kilograms of coal to run a 100-watt light bulb 24 hours a day for a year.
That's equal to the weight of three baby elephants!


How many UK 100-watt light bulbs could you run for 12 hours a day with 12 baby elephants' weight of coal?

answer is 8

[mystery]

Well it is 4 times as much coal, and half as much time, so that is why it is 8 bulbs.

[goldenstar]

Thank you very much.