Question:easy

How many 3-digit numbers can be formed using three distinct single digit prime numbers?

Show Hint

First list all single-digit prime numbers, then count the ways to arrange three distinct ones in order.
Updated On: Aug 7, 2026
  • 64
  • 24
  • 12
  • 4
Show Solution

The Correct Option is B

Solution and Explanation

This is a direct counting problem, best solved by filling the three digit slots of the number one at a time, from left to right, using the slot-filling (multiplication) method instead of the permutation formula directly.

  1. Find the pool of digits: Among the digits $0$ through $9$, the prime numbers are $2, 3, 5, 7$. That gives a pool of exactly $4$ digits to pick from, and since $0$ is not prime, every number built from these digits is automatically a valid 3-digit number with no leading-zero problem.
  2. Fill the hundreds place: Any of the $4$ primes can go here, so there are $4$ options.
  3. Fill the tens place: The digits must be distinct, so one prime has already been used in the hundreds place. That leaves $3$ primes for the tens place.
  4. Fill the units place: Two primes are now used up, leaving $2$ primes for the units place.

Multiplying the choices for each slot gives the total count of distinct numbers: $4 \times 3 \times 2 = 24$.

Let's summarize:

  • There are only $4$ single digit primes: $2, 3, 5, 7$.
  • Filling three slots one at a time with shrinking choices ($4$, then $3$, then $2$) gives $24$ total 3-digit numbers.

So $24$ distinct 3-digit numbers can be formed, matching option (B).

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