algebra · Year 7 · Suggested learning sequence
Substituting into expressions
Substituting means swapping a letter for a number and working out the value. Remember that a number written next to a letter means multiply: 3n means 3 × n, not 3 + n and not the digits stuck together. So if n = 4, then 3n + 2 means 3 × 4 + 2 = 12 + 2 = 14. Do the multiplying first (following the order of operations), then add the extra number. Say '3n' out loud as 'three lots of n' to keep the times sign in mind.
Sample questions
If n = 3, find 2n + 4.
- Substitute n = 3: 2n means 2 × 3.
- 2 × 3 = 6.
- 6 + 4 = 10.
Answer: 10
If n = 2, find 2n + 3.
- Substitute n = 2: 2n means 2 × 2.
- 2 × 2 = 4.
- 4 + 3 = 7.
Answer: 7
If n = 5, find 2n + 2.
- Substitute n = 5: 2n means 2 × 5.
- 2 × 5 = 10.
- 10 + 2 = 12.
Answer: 12