Answer:
40
Step-by-step explanation:
Given that
Total number of adults, U = 285
Number of plane travellers, P = 75
Number of train travellers, T = 55
To find the number of people that didn't travel by any means of transportation listed in the question, then we say
Total number of adults minus number people who traveled by plane or train minus number of people who traveled by bus but not by plane or train.
This means that number of people who didn't travel by any of the three means of transportation, N =
N = U - pt - b
N = 285 - 215 - 30
N = 40
Therefore, the total number needed is 40
