What is substitution?
Substitution means swapping a letter for a number, then calculating.
Substitution is one of the most useful moves in algebra. It simply means replacing a letter with a number, then working out the answer.
Think of an expression like as a vending machine slot. The letter is a gap waiting for a number. If you decide , you drop a 3 into the gap and the expression becomes .
The method is always the same:
- Write the expression.
- Replace each letter with its given number.
- Work out the answer, following BIDMAS.
One quiet trap is the hidden multiplication sign. Remember means . So if , then — it is not the digits stuck together to make 34. Putting the multiplication sign back in as you substitute keeps you safe.
- Substitution means replacing a letter with a number.
- Swap in the value, then calculate the answer.
- means — put the times sign back in.
- Always follow BIDMAS once the numbers are in.