5
Review: letter and number expressions
Textbook: Part 1, lesson 5, pp. 12–13
GoalReview number and letter expressions; finding the value by replacing a letter with a number.
New words
expression · ifodaletter expression · harfiy ifodaits value · qiymatibrackets · qavs
Explanation
In a letter expression we replace the letter by a number to find the value. If a is the number of cows and b the number of sheep, then a + b is both together and a − b tells how many more cows than sheep. The operation in brackets is done first.
Worked examples
If a = 9 and b = 4: a + b = 13 and a − b = 5.
(12 − 6) + 9 = 6 + 9 = 15; 20 − (18 + 2) = 20 − 20 = 0.
Class activity
“Letter cards”: cards with a, b, c are placed next to number cards. A child picks cards and says the value of a + b.
Practice
1
a = 9, b = 4. a + b = ?
13
2
a = 9, b = 4. a − b = ?
5
3
(12 − 6) + 9 = ?
15
4
Yesterday 43 eggs were collected and today 2 more, that is 45. How many in two days?
88