Question:medium

How many 3-digit numbers are there, for which the product of their digits is more than 2 but less than 7?

Updated On: Jun 26, 2026
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Solution and Explanation

Let the 3-digit number be represented as \( abc \), where \( a, b, c \) are its digits.

The condition is:

\[ 2 < a \times b \times c < 7 \]

The possible values for the product \( a \times b \times c \) are:

\[ 3,\ 4,\ 5,\ 6 \]

Case 1: Digits (1, 1, x)

The product is \( 1 \times 1 \times x = x \). Valid values for \( x \) are 3, 4, 5, 6. This yields 4 sets of digits:

  • (1,1,3)
  • (1,1,4)
  • (1,1,5)
  • (1,1,6)

Each set can form \( 3!/2! = 3 \) distinct numbers. Total numbers from this case: \( 4 \times 3 = 12 \).

Case 2: Product = 4

The digits must be (2,2,1). The number of distinct arrangements is:

\[ \frac{3!}{2!} = 3 \]

Case 3: Product = 6

The digits must be (1,2,3). Since all digits are distinct, the number of permutations is:

\[ 3! = 6 \]

Total Count:

The total number of valid 3-digit numbers is the sum of numbers from each case:

\[ 12 + 3 + 6 = \boxed{21} \]

Final Answer:

21 valid numbers satisfy the condition \( 2 < a \times b \times c < 7 \).

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