Named numbers: arithmetic with them
Add, subtract, multiply and divide named numbers: write them in one unit, do the sum and write the result in two units.
- Germany: grade 3
- Ukraine: grade 4
- Russia: grade 4
Guide
A named number is a number with the name of a unit, for example 2 m 40 cm or 3 kg 600 g. In Grade 4 all four operations are done with named numbers.
Method: write the named numbers in one (the smaller) unit, do the sum with ordinary numbers, then express the result in two units. For example 2 m 40 cm · 3 = 240 cm · 3 = 720 cm = 7 m 20 cm.
Reminder: 1 m = 100 cm, 1 kg = 1000 g. A common slip is to do the operation with one unit only, for example to multiply only the centimetres.