143
Year review: part–whole, segments
Textbook Part 4, pp. 66–67
GoalPart–whole problems; measuring and comparing segments; saying an expression in words.
New words
subtracting a sum from a number · sondan yig‘indini ayirishadding a sum to a number · songa yig‘indini qo‘shishchain · zanjir
Explanation
We read expressions in words: 45 − (12 + 13) is “subtracting a sum from a number”; 23 + (15 + 21) is “adding a sum to a number”; 66 − (54 − 42) is “subtracting a difference from a number”. Brackets first, then the rest.
Worked examples
28 pupils in a class; 16 ate samsa: 16 + x = 28 → x = 12 ate something else.
AB = 7 cm, CD = 4 cm: AB is 3 cm longer than CD.
Class activity
On the theme of “Meals”, each group writes 2 problems (e.g. bread, apples, juice in the canteen) and swaps with another group.
Practice
1
16 + x = 28. x = ?
12
2
Say in words: 50 + (20 + 5)
Adding a sum to a number = 75
3
66 − (54 − 42) = ?
54
4
Continue the chain: 5, 15, 25, 35, _
45