How many three-digit integers between 310 and 400, exclusive, are divisible by 3 when the ones digit and the hundered digit are switched?
Choose the correct choice:
A) 3  B) 19  C) 22  D) 30  E) 90
Answer is 30   No of digits between 310 and 400 (exclusive) = 400-310-1= 
<gadget id="calculator">400-310-1</gadget>
<output>89</output>
89   No Intergers divisble by 3=~ 89/3 ~ 30   Divsiblivity rule for 3 is Sum of all digits must be divisble by 3. It doesn't matter if hundred digit and ones digits are switched.   e.g 372 is divisble by 3 (becae 3+7+2= 
<gadget id="calculator">3+7+2</gadget>
<output>12</output>
12 (divisble by 3))   switch digits 732 also divisble by 3 (becae 7+3+2= 
<gadget id="calculator">7+3+2</gadget>
<output>12</output>
12 (divisble by 3))   Divsiblivity rule for 3 is Sum of all digits must be divisble by 3. It doesn't matter if hundred digit and ones digits are switched.   You have right. So it is enough to proceed like usual to find the numbers in a given range that are divisible by 3. So 399-312/3 +1=30.   Answer : 30
<result>D</result>
How many three-digit integers between 310 and 400, exclusive, are divisible by 3 when the ones digit and the hundered digit are switched?