30
Subtracting (43 − 16)
Textbook: Part 1, lesson 29, pp. 62–63
GoalLearn subtracting in parts (43 − 16) and finding mistakes.
New words
subtracting in parts · bo‘lib ayirishconfectionery · qandolatchilikcream · kremmistake · xato
Explanation
We subtract the tens and then the ones of the subtrahend: 33 − 18 = (33 − 10) − 8 = 23 − 8 = 15. When subtracting the ones we can again go down to a ten: 23 − 8 = (23 − 3) − 5 = 15. We check the answer by adding.
Worked examples
56 − 28 = (56 − 20) − 8 = 36 − 8 = 28.
71 − 25 = (71 − 20) − 5 = 51 − 5 = 46.
Class activity
“Spot the mistake”: the teacher writes a wrongly solved sum on the board (for example 52 − 18 = 46). Children find the mistake and give the right answer (34).
Practice
1
44 − 36 = ?
8
2
82 − 44 = ?
38
3
26 − x = 18. x = ?
8
4
A cake had 80 sugar balls. 35 went on the first layer and 27 on the second. How many are left?
18