101
Adding and subtracting on the number ray
Textbook: Part 3, lesson 101, pp. 101–103
GoalMoving along the number ray: adding means moving right, subtracting means moving left.
New words
move, shift · siljishto the right · o‘nggato the left · chapgato jump · sakramoq
Explanation
Movement on the number ray is described by addition and subtraction. Adding moves the point right, subtracting moves it left. The first number of the expression is the starting position, and each next number with its sign is one move. For example 5 + 7 − 3: start at 5, move 7 right to 12, move 3 left to 9. The result is the final position, i.e. its coordinate. If the value of a division is 4, one division stands for 4 units.
Worked examples
A dancer stands at 4 m on the stage, steps 9 m right, then 6 m left: 4 + 9 − 6 = 7 m.
On a ray, from 20 take 4 steps left, each of 3: 20 − 4 × 3 = 20 − 12 = 8.
Class activity
“The jumper”: a ray from 0 to 20 is drawn on the floor or board. One child says an expression (for example 6 + 8 − 5), another moves along the ray and finds where they stop.
Practice
1
A point stands at 12. It moves 7 right, 5 left and 3 right again. At which number does it stop?
17
2
A dancer stands 4 m from the left edge of the stage. She walks 9 m right and then 6 m left. How many metres is she now from the left edge?
7
3
Use the number ray to calculate: 9 − 4 + 6 − 8 + 5.
8
4
Starting from 20, 4 steps of 3 are taken to the left. Which number is reached?
8
5
Nilufar jumped from 2 to 10, Shahlo from 5 to 11, Ozoda from 9 to 16. Who jumped the farthest?
Nilufar (8 units)