If x + A = B, what is x?There is another important basic rule of algebra - what to do if there is something added to our unknown.
In this case, imagine you are carrying a heavy backpack. You know that it is full of various things and weighs 20kg. In order to lighten it, you want to take something out. The only thing you can spare is a large book that weighs 3kg. How much does your backpack weigh without it? 17kg, right. Believe it or not, that is algebra!
Let's write this in a more "algebraic" way:
- weightofbag + 3 kg = 20 kg
- weightofbag + 3 kg - 3 kg = 20 kg - 3 kg
weightofbag = 17 kg
- weightofbag + weightofbook = weightofheavybag
- weightofbag = weightofheavybag - weightofbook