How many positive integers less than 50 are multiples of 2 but NOT multiples of 5?
Select:
A) 4 B) 6 C) 8 D) 10 E) 20
IMO the answer is C (8 numbers)   The LCM of 2 and 5 is 10.   If x &lt;50 and x is divisible by 2 not by 5 --&gt; x is NOT divisible by 10.   From 1--&gt; 50, we have 5 numbers which is divisible by 10: 10, 20, 30, 40, 50.   From 1--&gt;50, we have (50-2)/2 +1= 
<gadget id="calculator">(50-2)/2 +1</gadget>
<output>25</output>
25 numbers divisible by 2.   Therefore, our answer is 25-5= 
<gadget id="calculator">25-5</gadget>
<output>20</output>
20 numbers.   20
<result>E</result>
How many positive integers less than 50 are multiples of 2 but NOT multiples of 5?