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Correct answer: 50
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We need the number of 3-digit numbers divisible by and , but not divisible by and .
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A number divisible by both and must be divisible by So first count 3-digit multiples of .
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The 3-digit numbers run from to .
The first 3-digit multiple of is and the last is . Thus the count is
- Now exclude those divisible by or . Since we are already among multiples of :
- divisible by and means divisible by
- divisible by and means divisible by
So from the 150 multiples of , remove 3-digit multiples of or .
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Count 3-digit multiples of : First is , last is .
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Count 3-digit multiples of : First is , last is .
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Numbers counted in both are divisible by both and , i.e. divisible by Count 3-digit multiples of : First is , last is .
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By inclusion-exclusion, numbers divisible by or are
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Therefore required count is
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Equivalently, these are 3-digit numbers divisible by but by neither nor .
So the final integer answer is
- Comparison with stored answer:
- Derived answer:
- Stored correct answer:
These do not match. The stored answer appears incorrect.
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