28
The number ray
Textbook: Part 1, lesson 28, pp. 87–89
GoalDraw a number ray, choose a unit segment and solve inequalities on the ray.
New words
number ray · koordinata nuriunit segment · birlik kesmadivision · bo‘linmainequality · tengsizlik
Explanation
A number ray has an origin, a direction and a unit segment. We pick a handy unit segment: if one division stands for 30 loaves, the marks are 0, 30, 60, 90, … The coordinate of a point tells how many unit segments it is from the origin. To solve an inequality on the ray, mark the points that fit the condition.
Worked examples
An oven bakes 30 loaves per hour. On the ray 0, 30, 60, 90, 120: 3 hours is 3 divisions, that is 90 loaves.
The natural solutions of 3 < x ≤ 7 are 4, 5, 6, 7 (four numbers).
Class activity
“People on the ray”: a ray is chalked on the ground; children stand at called-out coordinates and say the distance between them.
Practice
1
On a ray one division stands for 30 loaves. How many loaves is the 4th mark from the origin?
120
2
How many natural solutions does 3 < x < 9 have?
5
3
The unit segment is 3 cm. How many cm from the origin is the point with coordinate 7?
21
4
Points M(15) and N(40) are marked on a ray. How many unit segments long is MN?
25