Using the digits 1, 2, 3, 4, 5 and 6 with no digit repeated, how many even four-digit numbers greater than 3000 can be formed?
Answer and explanation
Correct answer: D. 120
- Step 1: The thousands digit must be 3, 4, 5 or 6. Split by whether it is even (4 or 6) or odd (3 or 5).
- Step 2: Even first digit: 2 choices, then the last digit must be one of the 2 remaining even digits, then the middle two digits come from 4 left: 4 x 3 = 12. Count = 2 x 2 x 12 = 48.
- Step 3: Odd first digit: 2 choices, last digit 3 even choices, middle 12. Count = 2 x 3 x 12 = 72.
- Step 4: Total = 48 + 72 = 120.
Answer
120.
Why not the others: 144 counts three even last digits for every first digit; 108 and 96 drop one of the two cases.
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