How to see it
An equation is a balance. Whatever you do to one side, do to the other. To solve it, undo the steps in reverse. The last thing done was add 7, so take away 7 first. Then undo the doubling by halving.
A worked example
2n plus 7 equals 25. Take 7 from both sides: 2n equals 18. Halve both sides: n equals 9. With brackets: 2 lots of x take 3 equals 14. Divide both by 2: x take 3 equals 7. Add 3: x equals 10.
The common mistake: undoing in the wrong order
The trap is undoing in the wrong order. Divide by 3 before taking 5, and you get messy fractions. If your answer is not a nice number, check the order. Always check by putting it back.
Try one
4x take away 3 equals 29.
- A6.5
- B8
- C26
- D32
Show the answerHide the answer
Right: B, 8
Add 3 to get 4x equals 32, then divide by 4.