19
Subtracting multi-digit numbers (practice)
Textbook: Part 1, lesson 19, pp. 58–60
GoalPractise subtraction of multi-digit numbers; kilometres and metres, length of a broken line.
New words
broken line (polyline) · siniq chiziqsegment of a broken line · bo‘g‘inmap scale · xarita masshtabikilometre · kilometr
Explanation
Before calculating with lengths we change them to one unit: 11 km 340 m = 11 000 m + 340 m = 11 340 m. The length of a broken line is the sum of the lengths of all its segments. If 1 cm on a map stands for a certain distance, multiply the map length by that number to get the real distance.
Worked examples
8 km 615 m = 8 000 m + 615 m = 8 615 m.
On a map 1 cm = 20 km. A road of 9 cm is 9 × 20 = 180 km in reality.
Class activity
“Travel map”: each group draws a broken line with 4 segments in a notebook, measures each segment in millimetres and finds the total length.
Practice
1
How many metres is 8 km 615 m?
8615
2
90 000 − 36 485 = ?
53515
3
On a map 1 cm stands for 20 km. A road is 9 cm on the map. How long is it in km?
180
4
The segments of a broken line are 45 mm, 38 mm, 27 mm and 56 mm. What is its length in mm?
166
5
The old road is 418 km. The new road is 65 km shorter. How long is the new road in km?
353