Idea 17of 23Builds onSolve it on the balance
The unknown can be on either side
Does the unknown have to be on the left?
Today you'll discover
- how to read 30 = x + 12
- why the same moves still work
- how to check it
Think first30 = x + 12
30 = x + 12. What is x?
Decide first, then press Next. Find the side with x, then do the same to both sides.
A level pan balance with a 30 block on the left and a box marked x and a 12 block on the right. 12 lifts off both pans, leaving 18 against x. Then 18 goes in the box: 18 + 12 = 30 on both sides. The last step shows 45 = 3x + 9.
See the whole ideathe big idea and the key word, in one place
The big idea
The unknown can be on either side; the equation means the same either way round.
For exampleStories often put the unknown on the right: “50 is 15 more than n” is 50 = n + 15, and n = 35.
Easy to get wrongThe number alone on one side is not the answer: in 30 = x + 12, x is 18, not 30.
Key word
- unknown
- the number an equation asks for, written with a letter
Ready to use it?
- Solve equations with the unknown on the right.