Idea 15of 23Builds onDo the same to both sidesWork backwards to the unknown
Solve it on the balance
How does a balance help you solve 2x + 4 = 18?
Today you'll discover
- what to take off first
- how to share what is left
- how to check on the balance
Think firstTwo boxes and a 4 balance 18
2x + 4 = 18. What is one box worth?
Decide first, then press Next. Take off, then share out, keeping the pans level.
A level pan balance: two boxes marked x and a 4 block on the left, an 18 block on the right. The 4 lifts off both pans, leaving two boxes against 14. Then 14 becomes two 7 blocks, one for each box. Then 7 goes back in each box: 2 × 7 + 4 = 18 on the left, 18 on the right. The last step shows 3x + 2 = 20.
See the whole ideathe big idea and the key word, in one place
The big idea
Take the same amount off both pans, then share what is left among the boxes.
On the balance
Every line is still level.
- start2x + 4 = 18
- − 42x = 14
- ÷ 2x = 7
Where it goes nextThis is working backwards, in a picture: taking off 4 undoes + 4, and sharing into 2 undoes 2 ×.
Key word
- isolate
- get the letter alone on one side of an equation
Ready to use it?
- Solve two-step equations like 2x + 4 = 18.