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16 Sep 2014, 00:38
Kudos
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Comet A appears near Earth every 12 years, while Comet B appears every 20 years. If both comets were last observed near Earth in 1979, how many years after 2004 will they both be visible near Earth at the same time?
A. 16
B. 20
C. 25
D. 32
E. 35
A. 16
B. 20
C. 25
D. 32
E. 35
16 Sep 2014, 00:38
Kudos
Bookmarks
Official Solution:
Comet A appears near Earth every 12 years, while Comet B appears every 20 years. If both comets were last observed near Earth in 1979, how many years after 2004 will they both be visible near Earth at the same time?
A. 16
B. 20
C. 25
D. 32
E. 35
The least common multiple of 12 and 20 is 60. This implies that the two comets appear together every 60 years. Consequently, the next year both comets will be visible simultaneously is 1979 + 60 = 2039. So, after 2004, in 35 years, they will both be visible near Earth at the same time.
Answer: E
Comet A appears near Earth every 12 years, while Comet B appears every 20 years. If both comets were last observed near Earth in 1979, how many years after 2004 will they both be visible near Earth at the same time?
A. 16
B. 20
C. 25
D. 32
E. 35
The least common multiple of 12 and 20 is 60. This implies that the two comets appear together every 60 years. Consequently, the next year both comets will be visible simultaneously is 1979 + 60 = 2039. So, after 2004, in 35 years, they will both be visible near Earth at the same time.
Answer: E
07 Jul 2021, 22:48
Kudos
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The comets are seen near Earth at different times; but we want to see them at the same time, therefore, we want them to be near Earth in a common year. This is ample evidence that we have to find out the LCM of 12 and 20.
The LCM of 12 and 20 is 60. Therefore, the comets are seen together once in every 60 years.
They were seen together in 1979, therefore, they will be seen again in 2039.
Since now is 2004, we will have to wait till 2039 (assuming we will be alive by then
)
The correct answer option is E.
Hope that helps!
Aravind BT
The LCM of 12 and 20 is 60. Therefore, the comets are seen together once in every 60 years.
They were seen together in 1979, therefore, they will be seen again in 2039.
Since now is 2004, we will have to wait till 2039 (assuming we will be alive by then
)The correct answer option is E.
Hope that helps!
Aravind BT
