2001 AMC 8 Problems/Problem 4

Problem

The digits 1, 2, 3, 4 and 9 are each used once to form the smallest possible even five-digit number. The digit in the tens place is

$\text{(A)}\ 1 \qquad \text{(B)}\ 2 \qquad \text{(C)}\ 3 \qquad \text{(D)}\ 4 \qquad \text{(E)}\ 9$

Solution 1

Since the number is even, the last digit must be $2$ or $4$. To make the smallest possible number, the ten-thousands digit must be as small as possible, so the ten-thousands digit is $1$. Simillarly, the thousands digit has second priority, so it must also be as small as possible once the ten-thousands digit is decided, so the thousands digit is $2$. Similarly, the hundreds digit needs to be the next smallest number, so it is $3$. However, for the tens digit, we can't use $4$, since we already used $2$ and the number must be even, so the units digit must be $4$ and the tens digit is $9, \boxed{\text{E}}$ (The number is $12394$.)

Solution 2 (Faster)

We know that the smallest possible number is $12349$. However, $12349$ is an odd number. Thus, by shifting the 4 (the largest even number) into the unit's place and rearranging the rest of the digits from least to greatest, we arrive at $12394$. Thus, the digit in the tens place is $\boxed{\text{E}}$ $9$.

See Also

2001 AMC 8 (ProblemsAnswer KeyResources)
Preceded by
Problem 3
Followed by
Problem 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
All AJHSME/AMC 8 Problems and Solutions

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