Question:medium

The number of numbers between \(2000\) and \(5000\) that can be formed with the digits \(0,1,2,3,4\), repetition of digits not allowed, and are multiples of \(3\), is

Show Hint

For divisibility by \(3\), first check the sum of digits. In digit-arrangement questions, decide the digit set first, then apply restrictions on the first digit.
Updated On: Jun 26, 2026
  • \(48\)
  • \(30\)
  • \(24\)
  • \(32\)
Show Solution

The Correct Option is B

Solution and Explanation

Step 1: Identify the structure of required numbers.
We need 4-digit numbers between 2000 and 5000 using digits $\{0,1,2,3,4\}$ without repetition. The thousands digit must be 2, 3, or 4 (it cannot be 0 since that gives a 3-digit number, and it cannot be 5 or above since we only have digits up to 4, and numbers must stay below 5000 with 4 in thousands giving exactly 4000s range which is still below 5000).
Step 2: Apply divisibility rule for 3.
A number is divisible by 3 if and only if the sum of its digits is divisible by 3. The total sum of all five available digits is $0+1+2+3+4=10$. Since we pick 4 out of 5 digits, exactly one digit is excluded. The sum of chosen digits equals $10 - (\text{excluded digit})$.
Step 3: Find which digit to exclude.
We need $10 - r \equiv 0 \pmod{3}$, which means $r \equiv 10 \equiv 1 \pmod{3}$. Among $\{0,1,2,3,4\}$, the digits congruent to 1 mod 3 are $r=1$ (since $1 \equiv 1$) and $r=4$ (since $4 \equiv 1$). So the excluded digit is either 1 or 4.
Step 4: Count valid numbers when digit 1 is excluded.
Remaining digits are $\{0,2,3,4\}$. The thousands digit can be 2, 3, or 4 (not 0), giving 3 choices. The remaining 3 positions are filled with the other 3 digits in any order: $3! = 6$ ways. Total for this case: $3 \times 6 = 18$.
Step 5: Count valid numbers when digit 4 is excluded.
Remaining digits are $\{0,1,2,3\}$. The thousands digit can be 2 or 3 only (not 0, and not 4 since 4 is excluded; also 1 in thousands gives 1000s which is below 2000). So thousands digit has 2 choices. The remaining 3 positions are filled with the other 3 digits: $3! = 6$ ways. Total for this case: $2 \times 6 = 12$.
Step 6: Add both cases for the final answer.
Total numbers = $18 + 12 = 30$. This matches option (2).
\[ \boxed{30} \]
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