How many integers between 3000 and 4000 that have distinct digits and increase from left to right ?
Choices
A) 20 B) 48 C) 60 D) 120 E) 600
Since the numbers must be distinct and increasing from left to right,   The only arrangements we could come-up with are:   345_ --&gt; 4   346_ --&gt; 3   347_ --&gt; 2   348_ --&gt; 1   356_ --&gt; 3   357_ --&gt; 2   358_ --&gt; 1   367_ --&gt; 2   368_ --&gt; 1   378_ --&gt; 1   Number of integers =20   So the answer is 20.
<result>A</result>
How many integers between 3000 and 4000 that have distinct digits and increase from left to right ?