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Number and letter expressions
Textbook Part 4, pp. 40–41
GoalTell number expressions from letter expressions; write a letter expression for a problem.
New words
number expression · sonli ifodaletter expression · harfiy ifodaunknown value · noma’lum qiymat
Explanation
An expression made of numbers and signs is a number expression: 12 + 5. If it also contains a letter, it is a letter expression: a + 5. The letter stands for an unknown or changing number. Put a number in place of the letter and you can work it out: if a = 3, then a + 5 = 8.
Worked examples
Mum bought a kg of oranges and b kg of apples. In all: a + b kg.
20 kg of cherries were picked and d kg went into jam. Left: 20 − d kg.
Class activity
“Mystery box”: a box holds some pebbles (unknown — x). The teacher adds 4. Children write x + 4. Then they open the box, find x and work out the value.
Practice
1
Which is a letter expression: 7 + 2 or c + 2?
c + 2
2
Mum poured k l of juice into a jug and 3 l stayed in the pan. Juice in all?
k + 3
3
If a = 6, then a + 9 = ?
15
4
If d = 8, then 20 − d = ?
12