A poplar tree was 3 feet high when it was planted on January 1, 1970. During what year did it pass the height of 20 feet?
(1) On January 1, 1973, it was 24 feet high.
(2) It doubled its height during each year.
Answer: B
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A poplar tree was 3 feet high when it was planted on January 1, 1970. During what year did it pass the height of 20 feet
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BTGModeratorVI
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Given: A poplar tree was 3 feet high when it was planted on January 1, 1970.BTGModeratorVI wrote: ↑Thu Nov 26, 2020 1:10 pmA poplar tree was 3 feet high when it was planted on January 1, 1970. During what year did it pass the height of 20 feet?
(1) On January 1, 1973, it was 24 feet high.
(2) It doubled its height during each year.
Answer: B
Source: GMAT prep
Target question: During what year did it pass the height of 20 feet?
Statement 1: On January 1, 1973, it was 24 feet high.
Important: This means the tree grew 24 feet in 3 years. HOWEVER, we cannot then conclude that the tree grew 8 feet each year, since we're given no information to suggest the tree grew at a constant rate.
This means the tree's height could have passed 20 feet in 1970, 1971, or 1972
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: It doubled its height during each year.
Perfect! We now know the following:
January 1, 1970: height = 3 feet
January 1, 1971: height = 6 feet
January 1, 1972: height = 12 feet
January 1, 1973: height = 24 feet
So, the tree's height passed 20 feet in 1972
Since we can answer the target question with certainty, statement 2 is SUFFICIENT
Answer: B
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deloitte247
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Target question => During what year did it pass the height of 20 feet?
Statement 1 => On January 1, 1973, it was 24 feet high
By 1973, it was already more than 20 feet but there is no information about the rate of growth, so the exact year it passed 20 feet is unknown so statement 1 is NOT SUFFICIENT
Statement 2 => It doubled its height during each year
Present height = 3ft; needed height = 20 - 3 = 17ft
Given that 1 year = previous height * 2. Then, for it to get to at least 18 feet, it will be in ;
=> 3 * 2 = 6 feet => 1971
=> 6 * 2 = 12 feet => 1972
=> 12 * 2 = 24 feet => 1973
Hence, the tree passed the height of 20 feet in 1973
Statement 2 alone is SUFFICIENT
Answer = B
Statement 1 => On January 1, 1973, it was 24 feet high
By 1973, it was already more than 20 feet but there is no information about the rate of growth, so the exact year it passed 20 feet is unknown so statement 1 is NOT SUFFICIENT
Statement 2 => It doubled its height during each year
Present height = 3ft; needed height = 20 - 3 = 17ft
Given that 1 year = previous height * 2. Then, for it to get to at least 18 feet, it will be in ;
=> 3 * 2 = 6 feet => 1971
=> 6 * 2 = 12 feet => 1972
=> 12 * 2 = 24 feet => 1973
Hence, the tree passed the height of 20 feet in 1973
Statement 2 alone is SUFFICIENT
Answer = B
