- A9
- B8
- C5
- D7
View written solutionFree
Correct answer: D
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Write the two progressions explicitly as APs
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First progression:
This is an AP with: Its -th term is
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Second progression:
This is an AP with: Its -th term is
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Find the last term included in each progression
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Up to the term of the first AP:
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Up to the term of the second AP:
So common terms must be numbers that appear in both APs and are therefore .
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Condition for a common term
A common term must satisfy: and also
Let . Then: Since , Hence: Therefore,
So the common terms form the sequence:
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Restrict to the given ranges
We need common terms that are present in both lists.
Since the second list goes only up to , we take common terms :
The next one is , so it is not included.
Thus, the number of common terms is:
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Check with options
Option is .
Final Answer:
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