Why convert to tonnes?

Thousands of kilograms are unwieldy, so dividing by one thousand gives tonnes that are easier to compare, and both units should be stated.

How is an electricity bill worked out?

Units times the price per unit is the bill, so find the units first rather than multiplying watts by the price.

Primary General Studies: Hong Kong Life and Environment Paper 4 (waste, recycling and electricity bills)

2026-11-03

P · r

Paper 4 scales daily waste per person up to a family, an estate and the whole city, then converts to tonnes and bills; each item needs two or three operations, but watch kilograms against tonnes and watts against units.

Quick answer　6 kg; 42 kg; 1 kg; $60; 3,500 kg; 1.2 tonnes; 36 tonnes; 110.5 trees; 14.4 units; $17.28; 11,250 tonnes; 4.106 million tonnes; 2,700 tonnes; one unit is 1,000 W for one hour.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10 questions
Suggested time	25 minutes
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: Primary General Studies: Hong Kong Life and Environment
Level	P6

02　Questions (10 items)

FoundationEach person throws away 1.5 kg a day. What does a family of four throw away in a day and in a week?
FoundationA plastic bottle weighs 25 g. What is the mass of forty bottles in kilograms?
FoundationElectricity costs $1.2 per unit. What is the bill for fifty units?
FoundationAn estate throws away 3.5 tonnes a day. How many kilograms is that?
IntermediateAn estate has 500 households throwing away 2.4 kg each a day. What is the daily total in tonnes, and over thirty days?
IntermediateRecycling one tonne of paper saves seventeen trees. How many trees does 6.5 tonnes save?
IntermediateA 60 W fan runs eight hours a day for thirty days. How many units does it use, and what is the bill at $1.2 per unit?
ChallengeAbout 7.5 million people each throw away 1.5 kg a day. What is the daily total in tonnes, and the yearly total in ten-thousands of tonnes?
ChallengeOf the 11,250 tonnes of daily waste, thirty per cent is food waste. How much is that, and how much of it is recoverable at eighty per cent?
Error redoError repair: a pupil says one unit of electricity is a 100 W appliance running for one hour. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	6 kg a day, 42 kg a week	One point five times four is 6 kg, and times seven is 42 kg.
2	1 kg	Twenty-five times forty is 1,000 g, and dividing by one thousand gives 1 kg.
3	HK$60	Fifty times 1.2 is 60, that is $60.
4	3,500 kg	One tonne is 1,000 kg, so 3.5 times 1,000 is 3,500 kg.
5	1.2 tonnes a day, 36 tonnes in thirty days	Five hundred times 2.4 is 1,200 kg that is 1.2 tonnes, and thirty days give 36 tonnes.
6	110.5 trees	Seventeen times 6.5 is 110.5 trees.
7	14.4 units, a bill of $17.28	Sixty times eight divided by one thousand is 0.48 units a day, times thirty is 14.4 units, and times 1.2 is $17.28.
8	11,250 tonnes a day, about 4.106 million tonnes a year	Seven point five million times 1.5 is 11.25 million kg that is 11,250 tonnes, and 365 days give 4,106,250 tonnes.
9	3,375 tonnes of food waste, 2,700 tonnes recoverable	Eleven thousand two hundred and fifty times 0.3 is 3,375 tonnes, and times 0.8 gives 2,700 tonnes.
10	one unit is 1,000 W for one hour	One unit is one kilowatt-hour, that is 1,000 W for one hour, so a 100 W appliance needs ten hours for one unit.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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