Question

On a certain day 40 trains each travelled between two of the towns M, N, O, P and Q. 10 trains travelled either from or to M. 10 trains travelled either from or to N. 10 trains travelled either from or to O. 10 trains travelled either from or to P. How many trains travelled from or to Q?
0
20
30
40

Answer 1

Answer:

40

Step-by-step explanation:

Key thing here that we need to bear in mind is that those 10 trains are different from each other, which means we cant use combination like MN, MO, MP and etc.  Because in that case we would be counting same train twice. in order to make each of those 10 trains distinguishable from each other is to make 1 common destination for all towns (which is Q). So its going to be:

MQ - 5 trains, QM - 5 trains  

NQ - 5 trains, QN - 5 trains

OQ - 5 trains, QO - 5 trains

PQ - 5 trains, QP - 5 trains

So, total number of trains which travelled either from or to Q will be 40.

Hope it helped.