How many positive three-digit integers are divisible by both 3 and 7?  Answers
A) 43 B) 45 C) 47 D) 50 E) 52
A number to be divisible by both 3 and 7 should be divisible by the least common multiple of 3 and 7 so by 21.   Multiples of 21 between 100 and 999, inclusive is   (last-first)/multiple+1=(987-105)/21+1=42+1= 
<gadget id="calculator">42+1</gadget>
<output>43</output>
43   43nswer: 43.
<result>A</result>
How many positive three-digit integers are divisible by both 3 and 7?