Oral methods: by digits, rounding, dividing in parts
Add and subtract by digits and by rounding, divide numbers by splitting them and divide round numbers in place-value units. Section: Grade 3; Grade 2 two-digit numbers are in another studio.
- Ukraine: grade 3
- Russia: grade 3
Guide
A studio for Ukrainian grade 3 (НУШ textbooks, parts 1 and 2): oral methods that come before written ones. Addition by digits: 346 + 238 is hundreds, tens and ones separately. The rounding method: 457 + 298 = 457 + 300 − 2.
Dividing in parts: 84 : 4 = (80 + 4) : 4 = 80 : 4 + 4 : 4 = 20 + 1. A two- or three-digit number is divided by a one-digit number after splitting it into handy addends. Corner division is taught only in grade 4.
Dividing round numbers in place-value units: 480 : 6 is 48 tens : 6 = 8 tens = 80. To divide by a round number, 600 : 30 means 60 tens : 3 tens = 20.
In each task a table shows the steps of the method; fill in the empty cells. The «why?» question asks you to compare methods.