How many positive integers of three different digits, each less than 400 can be formed from the digits 1, 2, 3, 4, 5 and 6?  Choose the correct choice:
A) 30  B) 60  C) 90  D) 120  E) 150
For the # to be &lt; 400 the 100s digit shud be &lt; 4 =&gt; one out of 3 choices 1/2/3   if the 100s digit is 1 then 10s digit can be selected in 5C1 and the units digit can be selected in 4C1 ways ==&gt; 5C1*4C1=20   the same is the case with 2 and 3 too.   hence answer is  20+20+20= 
<gadget id="calculator"> 20+20+20</gadget>
<output>60</output>
60   ANSWER:60
<result>B</result>
How many positive integers of three different digits, each less than 400 can be formed from the digits 1, 2, 3, 4, 5 and 6?