21 (a) A graph is drawn below: y | | | | | | +----------------- x Explain how you know that y is not directly proportional to x - OCR - GCSE Maths - Question 21 - 2017 - Paper 1

Since q is directly proportional to r, we can express this relationship as:

$q = k imes r$

where k is the constant of proportionality.

To find k, we can use the values given: 68 when r is 20:

$68 = k imes 20$

Solving for k gives:

$k = \frac{68}{20} = 3.4$

Now, substituting r = 25 into the equation:

$q = 3.4 \times 25 = 85$

Thus, when r is 25, q is 85.