Hi rakeshd347,

Mitch provides an explanation that TESTS THE ANSWERS, which is a great way to solve this problem. There's a Number Property rule that can actually make that solution a bit faster.

We're told that the average weight is 18 pounds, which makes the total weight 540 pounds (18 pounds x 30 boxes = 540 pounds)

Since the box weights are 10 or 20 pounds each, you can figure out the number of each.

If there were 30 20-pound boxes, the total weight would be 600 pounds.
Since the total weight is 540 pounds, that means that 6 of the boxes weight 10 pounds instead of 20.

So, there are:
6 10-pound boxes
24 20-pound boxes

Since we want to remove some number of the 20-pound boxes and get an average weight of 14 pounds, we know that the number of 10-pound boxes MUST BE greater than the number of 20-pound boxes (this is a weighted average Number Property). Since we have 6 10-pound boxes, we need to remove at least 19 20-pound boxes.

We can certainly TEST answer D first (which would eliminate the initial TEST that Mitch did and find the correct answer in 1 try) OR we can note that answer E (24) would eliminate ALL of the 20-pound boxes, which would make the average of the remaining boxes 10 pounds, which is too low (and would prove that answer D was correct).

GMAT assassins aren't born, they're made,
Rich