Callum is making pizza. He can choose three different toppings from:

• ham (H)
• sweetcorn (S)
• onion (O)
• mushrooms (M).
  List all the possible options for the three toppings. The first one has been done for you: HSO

Callum has four toppings to choose from: Ham (H), Sweetcorn (S), Onion (O), and Mushrooms (M). He needs to choose three different toppings for his pizza. This means for each combination, one topping will be left out. We can find all the combinations by considering which topping is excluded each time: 1. Exclude Mushrooms (M): The toppings are Ham, Sweetcorn, Onion. Combination: **HSO** (this was given). 2. Exclude Onion (O): The toppings are Ham, Sweetcorn, Mushrooms. Combination: **HSM**. 3. Exclude Sweetcorn (S): The toppings are Ham, Onion, Mushrooms. Combination: **HOM**. 4. Exclude Ham (H): The toppings are Sweetcorn, Onion, Mushrooms. Combination: **SOM**. The four possible combinations are HSO, HSM, HOM, and SOM.