In algebra, we use a letter to represent an unknown number.
Sometimes we need to substitute a number for the letter in an expression.
Example 1
Evaluate 2a - b when a = 6 and b = 7.
Answer 1
2a - b means (2 × a) - b
So this is (2 × 6) - 7
12 - 7 = 5.
Example 2
Work out the value of 5(x - 2) when x = 9.
Answer 2
Substitute x for 9 to get
5(9 - 2) which means 5 × (9 - 2).
Multiply everything inside the bracket with everything outside the bracket!
5 x 9 = 45
5 x -2 = -10
45 - 10 = 35
Algebra can look complicated but it will soon become second-nature to you.
The important thing is to take it one step at a time and write down all the stages.
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