135
Number and letter inequalities
Textbook Part 4, pp. 50–51
GoalFind numbers that make a letter inequality true; check properties of inequalities.
New words
letter inequality · harfiy tengsizliknumbers that work · mos keladigan sonlarnumber line · sanoq nuri
Explanation
In a letter inequality, several numbers may work in place of the letter. 7 + x < 13 is true for x = 0, 1, 2, 3, 4, 5; for x = 6 we get 13 < 13 — false. If 3 < 5, then 3 + 1 < 5 + 1 is also true.
Worked examples
Malika was ill more days than Nigora, and Nigora more than Amira. The most: Malika. On a number line: Amira, Nigora, Malika.
“The difference of 81 and y is greater than 40” → 81 − y > 40.
Class activity
Race a classmate: who finds fastest all the numbers that make x + 4 < 10 true? (0–5)
Practice
1
7 + x < 13. Which natural numbers work?
1, 2, 3, 4, 5
2
Write: “the sum of 7 and x is less than 13”.
7 + x < 13
3
Does x = 7 make x − 2 > 5 true?
No: 7 − 2 = 5, and 5 > 5 is false
4
If 8 > 6, then 8 + 10 ... 6 + 10
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