133
Working out the value of an expression
Textbook Part 4, pp. 46–47
GoalFind an expression’s value by putting a number in place of the letter; compare without calculating.
New words
value · qiymatto substitute · o‘rniga qo‘ymoqsecond · sekund
Explanation
To find the value of a letter expression, replace the letter with the given number and calculate. x + 11 when x = 17: 17 + 11 = 28. If the letter’s value is not given, the expression cannot be worked out.
Worked examples
At the start of the year x people joined a fitness group; now there are 11 more. If x = 17: 17 + 11 = 28 people.
Lola stood under the shower for 10 seconds and Kamola for 20: 20 − 10 = 10 seconds more.
Class activity
Points on a line: mark O; S 6 cm to the left of O; R 3 cm to the right; P between S and O; T to the right of R. Children count how many segments they get.
Practice
1
If x = 17, x + 11 = ?
28
2
Compare without calculating: 45 + 3 ... 45 + 13
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3
12 shoes are on the grass. How many children are walking barefoot?
6 (each has 2 shoes)
4
Which cannot be worked out: 20 + 5 or 20 + c?
20 + c (c is not known)