1
Review: numbers from 1 to 100
Textbook: Part 1, lesson 1, pp. 4–6
GoalReview adding and subtracting within 100 and finding an unknown addend.
New words
place (digit position) · xonacolumn · ustunequation · tenglamaconvenient method · qulay usul
Explanation
We add and subtract two-digit numbers place by place: ones first, then tens. If the ones add up to 10 or more, a ten is carried to the next place. If there are not enough ones to subtract, we borrow a ten. To find an unknown addend we subtract the known addend from the sum.
Worked examples
47 + 38: 7 + 8 = 15, write 5 and carry 1 ten; 4 + 3 + 1 = 8. Answer: 85.
x + 27 = 64, so x = 64 − 27 = 37. Check: 37 + 27 = 64.
Class activity
“Number chain”: the teacher says 50. Each child adds or subtracts a two-digit number of their choice and says the result. The next child continues from it.
Practice
1
58 + 27 = ?
85
2
93 − 48 = ?
45
3
x + 36 = 90 − 14. Find x.
40
4
A library has 64 storybooks and 29 poetry books. How many books are there in total?
93
5
Calculate in a convenient way: 23 + 49 + 17.
89