Math Problem Statement

A three‐digit number satisfies the following conditions: The digits are consecutive whole numbers in increasing order; the sum of each pair of digits is greater than 14 and less than 18; and the tens digit is an even number. What is the number?

Solution

Let the three-digit number be represented as xyzxyz, where xx, yy, and zz are the digits of the number. According to the conditions:

  1. The digits xx, yy, and zz are consecutive whole numbers in increasing order. Hence, we have: x=y1andz=y+1x = y - 1 \quad \text{and} \quad z = y + 1 So the number can be represented as (y1),y,(y+1)(y - 1), y, (y + 1).

  2. The sum of each pair of digits is greater than 14 and less than 18. We have three pairs to consider: x+y>14andx+y<18x + y > 14 \quad \text{and} \quad x + y < 18 y+z>14andy+z<18y + z > 14 \quad \text{and} \quad y + z < 18 x+z>14andx+z<18x + z > 14 \quad \text{and} \quad x + z < 18

    Substituting x=y1x = y - 1 and z=y+1z = y + 1 into these inequalities:

    • For x+yx + y: (y1)+y=2y1(y - 1) + y = 2y - 1 14<2y1<1815<2y<197.5<y<9.514 < 2y - 1 < 18 \quad \Rightarrow \quad 15 < 2y < 19 \quad \Rightarrow \quad 7.5 < y < 9.5 So y=8y = 8.

    • For y+zy + z: y+(y+1)=2y+1y + (y + 1) = 2y + 1 14<2y+1<1813<2y<176.5<y<8.514 < 2y + 1 < 18 \quad \Rightarrow \quad 13 < 2y < 17 \quad \Rightarrow \quad 6.5 < y < 8.5 Again, y=8y = 8.

    • For x+zx + z: (y1)+(y+1)=2y(y - 1) + (y + 1) = 2y 14<2y<187<y<914 < 2y < 18 \quad \Rightarrow \quad 7 < y < 9 So y=8y = 8.

  3. The tens digit yy is an even number, which is true since y=8y = 8.

Thus, the digits of the number are 77, 88, and 99, and the number is 789789.

The number is 789\boxed{789}.

Would you like more details or have any questions?

Here are some related questions:

  1. How do we solve inequalities for digit-based problems?
  2. What other types of sequences can we explore for digit-based puzzles?
  3. Can we use similar approaches for problems involving descending digits?
  4. How do we handle cases where the sum of digits involves different ranges?
  5. Are there alternative ways to verify the conditions of a solution?

Tip: Always simplify inequalities step-by-step to avoid miscalculations when solving for unknowns in digit problems.

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Math Problem Analysis

Mathematical Concepts

Number Theory
Inequalities
Consecutive Numbers

Formulas

Inequalities: x + y > 14 and x + y < 18

Theorems

Properties of consecutive numbers
Inequalities with digit sums

Suitable Grade Level

Grades 6-8