Hong Kong Primary 4 General Studies Practice Paper 2 with Answers | 10 questions, 45 minutes

When colds are going round, our teacher reminds us to wash our hands properly. Wetting your hands is not enough. You must use soap and rub your fingers, the gaps between them and your wrists for at least 20 seconds.
Why so long? Soap first dissolves the oil on your hands, then the water carries away the foam with the germs on it. That takes time. If you rub twice and rinse, the germs stay on your hands.
I kept a small record at home: I wash my hands about 8 times a day – before meals, after using the toilet and when I get home. At 20 seconds each time, that is 160 seconds, or 2 minutes 40 seconds.
A small thing adds up in one day.

Last month our estate put three new bins in the refuse room: blue for paper, yellow for metal and brown for food waste. The management office said that in the past all rubbish went into one bin, and now it must be sorted.
The cleaner told me our block has 40 households. Each household throws away about 2 bags a day and a bag weighs about 3 kg, so our block produces 240 kg of rubbish a day.
She said that once paper and metal are taken out, less rubbish goes to the landfill, and the paper can be made into new paper and the metal into new cans.
She also warned that if rice and leftovers are mixed in, the whole bag of paper cannot be recycled, so the sorting must be clean.

When you put an ice cube in water, it floats, and a small part of it stays above the surface.
Our teacher says water expands by about 9 per cent when it freezes, so ice is lighter than the same volume of water and floats.
She did an experiment: she poured 250 mL of water into a measuring cup and put it in the freezer. The ice took up about 22.5 mL more, making 272.5 mL, but the mass did not change at all.
That is why a glass bottle filled to the top may crack in the freezer.
For the same reason icebergs float in the sea, and only a small part of them shows above the water.