Hi petu,
This question is written in a very specific way - if you can catch the subtle clues in it, then you can answer this question relatively quickly.
We're told a few facts about a ferry:
1) It can hold UP TO 50 tons of cargo
2) HALF the vehicles on the ferry will be trucks while HALF the vehicles will be cars
3) Cars weigh an average of .75 tons each and trucks weigh an average of 5 tons each
We're asked for the GREATEST number of vehicles that the ferry can hold.
Since half the vehicles are trucks and half are cars, there will be an EQUAL number of each. By extension, that means there MUST be an EVEN number of vehicles (since 1+1=2, 2+2=4, 3+3=6, etc.).
Adding the weight of 1 car and 1 truck gets us .75 + 5 = 5.75 tons, so we really just have to figure out the MAXIMUM number of 5.75 "pairs" that go into 50 tons. You can do this math either by division OR by using the answers that are given, since one of them MUST be the answer.
Let's start with 16....that would be 8 "pairs" of vehicles.....8(5.75) is less than 8(6) = 48. So 16 vehicles COULD end up on the ferry. Since there is no other bigger answer that's EVEN, 16 must be the answer.
Final Answer:
GMAT assassins aren't born, they're made,
Rich