10
Adding and subtracting numbers
Textbook: Part 1, lesson 10, pp. 22–23
GoalSolving equations with three terms; comparing cm and dm.
New words
unknown · noma’lummap · xaritasegment · kesmamiddle (midpoint) · o‘rtasi
Explanation
In an equation with three terms we first add the known numbers: x + 10 + 12 = x + 22. Then we find the unknown. A segment of 10 cm equals 1 dm; its middle is 5 cm from each end.
Worked examples
x + 10 + 12 = 35 → x + 22 = 35 → x = 35 − 22 = 13.
Aziz has s maps and Anvar has d fewer: Anvar has s − d maps.
Class activity
“Middle of the segment”: children draw a 10 cm segment, find its middle with a ruler, mark point C and write its length in dm.
Practice
1
11 + y + 10 = 44. y = ?
23
2
z + 15 + 5 = 40. z = ?
20
3
There are 41 maps of Uzbekistan, 11 more than world maps. How many world maps?
30
4
How many dm is 10 cm?
1