How many 4-digit numbers (ABCD) can be formed such that |A – D| = 2? Choose the most appropriate option.
A) 2,000
B) 1,900
C) 1,800
D) 1,600
E) 1,500
Digit A can be filled in 9 ways (excluding 0)   Digit B can be filled in 10 ways   Digit 1,800 can be filled in 10 ways   Digit D can be filled in 2 ways (because of modulus A-D )   The answer will be  9*10*10*2= 
<gadget id="calculator"> 9*10*10*2</gadget>
<output>1_800</output>
1800   Ans 1,800
<result>C</result>
How many 4-digit numbers (ABCD) can be formed such that |A – D| = 2?