Expressions containing two letters
1.1. Knowledge to remember
For example : Two brothers fishing together. You caught… the fish. I caught… the fish. Both brothers caught… the fish.
The number of fish caught can be:
a + b is an expression that contains two letters.
 If a = 3 and b = 2 then a + b = 3 + 2 = 5; 5 is a value of the expression a + b.
 If a = 4 and b = 0 then a + b = 4 + 0 = 4; 4 is a value of the expression a + b.
 If a = 0 and b = 1 then a + b = 0 + 1 = 1; 1 is a value of the expression a + b.
Each time we replace the digit, we get a value of the expression a + b.
1.2. Solving Textbook Exercises
Lesson 1: Calculate the value of c+d if
a) c = 10 and d = 25; b) c = 15cm and d = 45cm.
Solution guide:
 Replace letters with numbers and calculate the values of those expressions.
a) If c = 10 and d = 25 then c+d = 10+25 = 35.
b) If c = 15cm and d = 45cm, then c+d = 15cm+45cm = 60cm.
Lesson 2: a−b is a twodigit expression. Calculate the value of a−b if
a) a = 32 and b = 20;
b) a = 45 and b = 36 ;
c) a = 18m and b = 10m.
Solution guide:
 Replace letters with numbers and calculate the values of those expressions.
a) If a = 32 and b = 20 then a−b = 32−20 = 12;
b) If a = 45 and b=36b=36 then a−b=45−36=9a−b=45−36=9 ;
c) If a = 18m and b = 10m, then a−b = 18m−10m = 8m.
Lesson 3: axb and a : b are expressions containing two letters
Write the expression value in a blank cell (according to the pattern):
a 
twelfth 
28 
60 
70 
b 
3 
4 
6 
ten 
axb 
36 



a : b 
4 


Solution guide:
 Replace letters with numbers and calculate the values of those expressions.
a 
twelfth 
28 
60 
70 
b 
3 
4 
6 
ten 
axb 
36 
112 
360 
700 
a : b 
4 
7 
ten 
7 
Lesson 4: Write the value of the expression in the empty cell
a 
300 
3200 
24 687 
54 036 
b 
500 
1800 
63 805 
31 894 
a + b 




b + a 



Solution guide:
 Replace letters with numbers and calculate the values of those expressions.
a 
300 
3200 
24 687 
54 036 
b 
500 
1800 
63 805 
31 894 
a + b 
800 
5000 
88 492 
85 930 
b + a 
800 
5000 
88 492 
85 930 
.
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