When we substitute a number for a letter, we simply replace the letter with the number.
Example
Work out the value of the following expression when a = 4 and b = 9
| a | + | b |
| 2 | 3 |
Answer
We substitute a = 4 and b = 9 into the following expression:
| a | + | b |
| 2 | 3 |
| = | 4 | + | 9 |
| 2 | 3 |
= 2 + 3 = 5
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