Basic Algebra II

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

Now, working like we did previously, we want to take this statement and act on it so that we get "weightofbag = something" This is easily doen if we subtract 3kg from both sides:

weightofbag + 3 kg - 3 kg = 20 kg - 3 kg

weightofbag = 17 kg

Now, we can write this more generally - we have a heavy bag that weighs weightofheavybag and we want to remove a book that weighs weightofbook, leaving us with a bag that weighs weightofbag:

weightofbag + weightofbook = weightofheavybag

then

weightofbag = weightofheavybag - weightofbook

Or, we can write this in more traditional algebra notation as: If x + A = B (where A and B are numbers that you are given) then x = B - A