17
Subtracting (50 − 22)
Textbook: Part 1, lesson 17, pp. 36–37
GoalLearn subtracting a two-digit number from a whole ten (50 − 22).
New words
minuend · kamayuvchisubtrahend · ayriluvchidifference · ayirmacompass · kompas
Explanation
In 50 − 22 there are too few ones. From 5 tens we change 1 ten into 10 ones: 4 tens 10 ones − 2 tens 2 ones = 2 tens 8 ones = 28. Check: 28 + 22 = 50.
Worked examples
60 − 27: 5 tens 10 ones − 2 tens 7 ones = 3 tens 3 ones = 33.
40 − 14 = 3 tens 10 ones − 1 ten 4 ones = 26.
Class activity
“The exchange bank”: show 50 − 22 with ten-rods and unit cubes, using a “bank” where one ten is exchanged for 10 ones.
Practice
1
70 − 39 = ?
31
2
80 − 46 = ?
34
3
40 notebooks arrived at school and 14 were given to Grade 1. How many are left?
26
4
A book has 90 pages. Karim has read 57. How many pages are left to read?
33