Fractions, SM-Bank 49 MC

A garden centre sells a potting mix made up of soil, manure and sand.

Soil makes up `3/4` of the mix and manure makes up `1/6` of the mix.

What fraction of the potting mix is sand?

1. `1/12`
2. `1/40`
3. `5/12`
4. `3/7`