The table below shows the number of clips in different coloured containers.

1. Express the ratio of the number of clips in white containers to blue containers

Ratio of clips in white containers to blue containers = $3 : 2$
Let the number of clips in white containers be $3u$ and the number of clips in blue containers be $2u$.

2. Find the number of white and blue containers in terms of units

Number of clips per white container = $30$
Number of white containers = $\frac{3u}{30} = \frac{u}{10}$

Number of clips per blue container = $50$
Number of blue containers = $\frac{2u}{50} = \frac{u}{25}$

3. Calculate the fraction of blue containers out of the total containers

Total number of containers = $\frac{u}{10} + \frac{u}{25} = \frac{5u}{50} + \frac{2u}{50} = \frac{7u}{50}$

Fraction of blue containers = $\frac{\frac{u}{25}}{\frac{7u}{50}} = \frac{u}{25} \times \frac{50}{7u} = \frac{2}{7}$