How do you do P5 unit conversion questions with decimals?
This page teaches converting a measurement from a smaller unit to a larger one in decimal form, and back again, for the four pairs of units the Primary 5 syllabus names.
What your child learns here
This page teaches converting a measurement from a smaller unit to a larger one in decimal form, and back again, for the four pairs of units the Primary 5 syllabus names. It rests on multiplying and dividing decimals by 10, 100 and 1000.
There are 1000 m in 1 km, 100 cm in 1 m, 1000 g in 1 kg and 1000 ml in 1 L.
Going from a larger unit to a smaller one, the number gets bigger, so multiply: 3.6 km is 3600 m.
Going from a smaller unit to a larger one, the number gets smaller, so divide: 75 cm is 0.75 m.
Multiplying or dividing by 10, 100 or 1000 moves the digits one, two or three places, with zeros as place holders where needed.
An answer less than 1 is written with a 0 before the decimal point, such as 0.08 kg for 80 g.
Does the answer make sense?
When the new unit is smaller, such as kilograms to grams, your child's number must get bigger, and when the new unit is larger it must get smaller. A thousand grams make one kilogram, so 48 g should become a tiny part of a kilogram, well under 1.
How to practise these questions
Basic questions train converting lengths, masses, distances and volumes between a larger and a smaller unit, deciding each time whether the number grows or shrinks. Intermediate work adds a volume under one litre turned into millilitres, where the size of the answer can surprise. Challenge questions need zeros held in place after the point, or several measures in mixed units put in order by converting them all first. If the decimal point keeps slipping, watch the solution film for that conversion and retry it later from Revision.
Questions parents ask
How many grams are in a kilogram, and millilitres in a litre? There are 1000 g in 1 kg and 1000 ml in 1 L. There are also 1000 m in 1 km, and 100 cm in 1 m.
Which unit conversions are in the Primary 5 syllabus? The syllabus lists four pairs: kilometres and metres, metres and centimetres, kilograms and grams, and litres and millilitres, converted in decimal form in both directions.
Why does the decimal point seem to move when we change units? Multiplying or dividing by 10, 100 or 1000 shifts each digit one, two or three places. The digits move past the point, which looks like the point moving.
