In this activity, we'll be learning how to change missing number problems into algebra.
So first... what is algebra?
We use algebra when we don't know the exact numbers in a calculation, and to do this we use letters to stand for numbers that we are trying to find.
Algebra is like a language with its own rules! Let's look at some of the rules we need to know.
1) a stands for a number (we can use any letter)
2) a + 2 is 2 more than the number.
3) a - 7 is 7 less than the number.
4) 5a is 5 times the number (we don't use the × sign in algebra because it looks like the letter x).
5) a/4 or ¼ a is a quarter of the number or the number divided by 4. (N.B. We don't use the ÷ sign in algebra.)
Let's now use our algebra knowledge to work out the following problem:
I think of a number.
1) I double it and 2) take away 5.
3) I get 21.
Write this using algebra.
Use n for the number I think of.
n is the number I think of.
1) Double it to get 2n (remember this means 2 times n)
2) Take away 5 to get 2n - 5
3) This equals 21, so we write:
2n - 5 = 21