Bunuel wrote:
Of the goose eggs laid at a certain pond, 2/3 hatched and 3/4 of the geese that hatched from those eggs survived the first month. Of the geese that survived the first month, 3/5 did not survive the first year. If 120 geese survived the first year and if no more than one goose hatched from each egg, how many goose eggs were laid at the pond?
(A) 280
(B) 400
(C) 540
(D) 600
(E) 840
STRATEGY: Upon reading any GMAT Problem Solving question, we should always ask, Can I use the answer choices to my advantage?
In this case, we can easily test the answer choices.
From here, I'd typically give myself up to 20 seconds to identify a faster approach, but I can already see that I can immediately in lemonade to answer choices, which means I only need to test one answer choice. We’re told that 2/3 of the goose eggs laid hatch.
Since the answer choices tell us the number of goose eggs laid, we can immediately eliminate choices A and B since 2/3 of 280 and 2/3 of 400 don’t result in integer values (and this real world question doesn’t allow for fractional hatchlings!).
From here, we’ll test choice D (the middle remaining choice). If it works, we’re done. If we end up with
more than 120 geese, then the correct answer must be C. If we end up with
fewer than 120 geese, then the correct answer must be E.
(D) 600 This tells us the number of goose eggs we start with.
Given: 2/3 of the eggs hatched. So, the total number of hatchlings = 2/3 of 600 =
400Given: 3/4 of the hatchlings survived the first month. So, the number of 1st month survivors = 3/4 of
400 =
300Given: Of the geese that survived the first month, 3/5 did not survive the first year, which means 2/5 of those geese survived.. So, the number of survivors = 2/5 of
300 =
120Perfect!! This matches the information in the question.
Answer: D