When estimating, compatible numbers are numbers that are close in value to the actual numbers, and which make it easy to do mental arithmetic.
Distance from A to B = B-A = 18-0 = 18
M is the midpoint which means it is equal distance between A and B
M = distance between A and B divided by 2:
M = 18/2 = 9
Answer: M = 9
6/6 or 1/1 of the pizzas where large or extra large
