How many positive integers less than 50 are multiples of 3 but NOT multiples of 5?
Answers:
A) 4	B) 6	C) 8	D) 10	E) 12
IMO the answer is C (8 numbers)   The LCM of 3 and 5 is 15.   If x &lt;50 and x is divisible by 3 not by 5 --&gt; x is NOT divisible by 15.   From 1--&gt; 50, we have 3 numbers which is divisible by 15: 15, 30, 45.   From 1--&gt;50, we have (45-3)/3 +1= 
<gadget id="calculator">(45-3)/3 +1</gadget>
<output>15</output>
15 numbers divisible by 3.   Therefore, our answer is 15-3= 
<gadget id="calculator">15-3</gadget>
<output>12</output>
12 numbers.   12
<result>E</result>
How many positive integers less than 50 are multiples of 3 but NOT multiples of 5?