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GMAT club Flashcards v7 questions [#permalink]
12 Dec 2012, 11:21
Hi All,
I am going through GMAT club Flashcards v7. I have difficulty understanding following questions. Please help !
Question 1 (page 21)
certain bacteria colony doubles in size every day for 20 days, at which point it reaches the limit of its habitat and can no longer grow. If two bacteria colonies start growing simultaneously, how many days will it take them to reach the habitat’s limit? 6.33 7.5 10 15 19
Its mentioned 
1 colony = x * 2^20
I think it should be x* 2^20 because 1st day the size is x then second it is 2x (x*2^1) and so on then 20th day it will be x*2^19 (0 to 20 the difference is 19)
Question 2 (page 13)
If a farmer sells 15 of his chickens, his stock of feed will last for 4 more days than planned, but if he buys 20 more chickens, he will run out of feed 3 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have? 12 24 48 55 60
The solution mentions  Solving the first equation, we get x=60 and y=12
Where is the first equation ? I can see only the below equation which gives x=5y
(x‐15)(y+4)=(x+20)(y‐3)
