Two angles of a triangle add up to 98°. What is the size of the third angle?

$$180^\circ - 98^\circ = 82^\circ$$

The size of the third angle is \boxed{\text{82^\circ}}.

2. What is the cost of 1 crate of eggs at 80 pesos each?

This question is incomplete. To calculate the total cost, we need to know how many eggs are in 1 crate. Without this information, a specific numerical answer cannot be provided.

3. How many groups of 4 make 20?

$$20 \div 4 = 5$$

There are $\boxed{\text{5}}$ groups of 4 in 20.

4. An orange cost £1.50. How much do 9 oranges cost?

$$£1.50 \times 9 = £13.50$$

9 oranges cost $\boxed{\text{£13.50}}$.