How many even 4-digit integers greater than 8000 are there such that all their digits are different? Choose the most appropriate option:
A) 240  B) 369  C) 469  D) 520  E) 599

Rationale: case 1 : numbers starting with 8 followed by even number the hundreds digit can take 4 numbers ( 0,2 , 4,6 ) so 4 ways the unit digit can take remaining 3 even numbers left after using 2 , to be even so 3 ways . the tens digit can take remaining 7 numbers left after using 3 numbers so 7 ways total = 4 * 3 * 7 = 84 case 2 : numbers starting with 8 followed by odd number the hundreds digit can take 5 numbers ( 1 , 3,5 , 7,9 ) so 5 ways the unit digit can take remaining 4 even numbers ( 0,2 , 4,6 ) to be even so 4 ways . the tens digit can take remaining 7 numbers left after using 3 numbers so 7 ways total = 5 * 4 * 7 = 140 case 3 : numbers starting with 9 followed by even number the hundreds digit can take 5 numbers ( 0 , 2,4 , 6,8 ) so 5 ways the unit digit can take remaining 4 even numbers left after using 1 , to be even so 3 ways . the tens digit can take remaining 7 numbers left after using 3 numbers so 7 ways total = 5 * 3 * 7 = 105 case 4 : numbers starting with 9 followed by odd number the hundreds digit can take 4 numbers ( 1,3 , 5,7 ) so 4 ways the unit digit can take 5 numbers ( 0 , 2,4 , 6,8 ) to be even so 5 ways . the tens digit can take remaining 7 numbers left after using 3 numbers so 7 ways total = 4 * 5 * 7 = 140 hence 84 + 140 + 105 + 140 = 469 , correct answer is c
Answer: C