10
Chapter I review problems
Textbook: Part 1, lesson 10, pp. 40–43
GoalReview Chapter I: numbers, rounding, addition and subtraction, expressions, equations.
New words
natural number · natural sonrounding · yaxlitlashvalue of an expression · ifodaning qiymatiroot of an equation · tenglamaning ildizi
Explanation
Natural numbers form the sequence 1, 2, 3, ...; 0 is not a natural number. Large numbers are read in classes and compared on the number ray and place by place. In rounding we take the nearest ten, hundred or thousand. Addition and subtraction are inverse operations; they are used to solve equations and to check results. The laws of addition make calculation easier. To solve a problem, first find what is known and unknown, form an equation, then find the root and check the answer.
Worked examples
Round 7 285 614 to hundred thousands: 7 200 000 < 7 285 614 < 7 300 000 and 85 614 > 50 000, so 7 285 614 ≈ 7 300 000.
After 450 kg was taken from a store, 1 280 kg was left. At first there were x kg: x − 450 = 1 280, x = 1 280 + 450 = 1 730 kg.
Class activity
“Chapter quiz”: the class splits into two teams. Teams take turns with questions on reading, comparing, rounding, equations and expression values; 1 point per correct answer.
Practice
1
Compute 56 478 + 9 522.
66000
2
Solve x − 239 = 761.
1000
3
After 450 kg was taken from a store, 1 280 kg was left. How many kg were there at first?
1730
4
Why does rounding 3 000 000 to hundred thousands give the number itself?
3 000 000 is already a round hundred-thousand: all places after the hundred thousands are zeros, so its distance to the nearest one is 0.