Common mistakes
Joining digits instead of multiplying
✕\(\displaystyle 3n=34\quad\text{when }n=4\)✓\(\displaystyle 3n=3\times4=12\)
A coefficient multiplies the assigned valueReplacing only one occurrence
✕\(\displaystyle n^2+n=4^2+n\quad\text{when }n=4\)✓\(\displaystyle n^2+n=4^2+4=20\)
Every occurrence of the same variable uses the same assigned valueLosing the grouped quantity
✕\(\displaystyle 3(n+5)=3\times6+5\quad\text{when }n=6\)✓\(\displaystyle 3(n+5)=3(6+5)=33\)
Keep the original brackets when replacing the letterDifficulty levels
introUse assigned whole numbers and an integer addition with a signed input
standardPreserve grouped quantities and match multiple inputs to their values
challengeUse exact fractional values in repeated-variable and multi-input expressions
Questions about this topic
Do I have to change a decimal to a fraction?+
No, if you can calculate exactly with the decimal. An equivalent fraction is useful when it prevents rounding
Can different letters have the same value?+
Yes. Use the assignments that are given, whether their values are equal or different
Is substitution the same as solving an equation?+
No. Substitution uses a supplied value. Solving finds a value that makes an equation true
Can I use a calculator?+
No. This topic is practised without a calculator
Which year level and chapter is this?+
Year 7 Mathematics, chapter 3: Algebra and coordinates