Free Direct and inverse proportion PDF Worksheets & Answers
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Explanation:
If y is directly proportional to x (written y ∝ x), then y = kx. If y is inversely proportional to x (written y ∝ 1x), then y = kx. Read the question carefully for powers or roots such as x2, x3, or √x.
Always follow three steps: (1) write the proportion equation with constant k, (2) substitute the given pair of values to find k and write the full formula, and (3) substitute the new value to find the unknown.
Example 1: y is directly proportional to x2. When x = 3, y = 45. Find y when x = 5.
Solution:
Example 2: y is inversely proportional to x. When x = 4, y = 15. Find x when y = 12.
Solution:
GCSE Past Paper Direct and inverse proportion Questions & Answers
y is directly proportional to x. [1 mark]
Worked Solution & Mark Scheme (2 marks)
The graph shows the relationship between R and t for 0 ≤ t ≤ 4
Worked Solution & Mark Scheme (5 marks)
at (2, 10), 10 = 4k ⇒ k = 2.5 ⇒ R = 2.5t² A1
⇒ t² = 16/(25x)
⇒ t = (4/5)/√x = 0.8/√x C1