Free Year 7 Substitute into a formula Practice | Skillo

Question 1 — Easy

Kofi is designing a square patio with a diagonal length of 8 metres. What is the area of the patio to the nearest square metre? (Use the relationship: area = diagonal² ÷ 2)

Answer: Area = 8² ÷ 2 = 64 ÷ 2 = 32 m².

Question 2 — Medium

Priya uses the formula v = u + at to find the final speed of a wombat in a science project. Given that u = −2, a = 5 and t = 4, calculate the value of v.

Answer: Substituting u = −2, a = 5 and t = 4 gives v = −2 + 5 × 4 = −2 + 20 = 18. Option A incorrectly treats u as positive: 2 + 20 = 22. Option C multiplies all three values together with the negative sign: −2 × 5 × 4 = −40. Option D adds all three values: −2 + 5 + 4 = 7.

Question 3 — Hard

Priya is organising a school fundraiser selling handmade bracelets. She spends $12 on materials to get started, and each bracelet costs an additional $3 in materials to make. Let b represent the number of bracelets Priya makes. Which algebraic expression represents the total cost, in dollars, of making b bracelets?

Answer: The total cost is the fixed starting cost of $12 plus $3 multiplied by the number of bracelets, giving 3b + 12. Option A ignores the fixed starting cost entirely. Option B incorrectly multiplies the fixed cost by b instead of treating it as a constant. Option D combines both values into a single coefficient, which is incorrect because the $12 is a one-off cost, not a per-bracelet cost.