28
Column addition and subtraction
Textbook: Part 1, lesson 27, pp. 58–59
GoalAdding and subtracting two-digit numbers in columns (no regrouping).
New words
column · ustunstep-by-step method · algoritmones · birliklartens · o‘nliklar
Explanation
In a column we write ones under ones and tens under tens. First we add or subtract the ones, then the tens, and read the answer. 12 + 46: ones 2 + 6 = 8, tens 1 + 4 = 5, answer 58.
Worked examples
35 − 14: ones 5 − 4 = 1, tens 3 − 1 = 2, answer 21.
97 − 6: ones 7 − 6 = 1, the 9 tens stay, answer 91.
Class activity
“Building columns”: children write digits in strict columns on squared paper. Partners check each other’s columns.
Practice
1
45 + 14 = ?
59
2
49 − 23 = ?
26
3
97 − 6 = ?
91
4
In a factory 46 robots weld and 22 robots assemble. How many robots in all?
68