A box contains only red, blue and green pens - OCR - GCSE Maths - Question 2 - 2018 - Paper 1

From the second ratio, let the number of blue pens be $1y$ and the number of green pens be $4y$. We know the number of blue pens from the previous step is $9x$, thus we can equate:

$1y = 9x \implies y = 9x$

Now substituting $y$ gives:

• Green pens = $4y = 4(9x) = 36x$.

Now, summing up the total number of pens:

$\text{Total pens} = 5x + 9x + 36x = 50x$

The number of blue pens is $9x$. Therefore, the percentage of blue pens can be calculated as:

$\text{Percentage of blue pens} = \left( \frac{9x}{50x} \right) \times 100 = \frac{9}{50} \times 100 = 18\%$