9?5-?3?=402

Interpret the problem as filling digits in two 3-digit numbers:

• 9a5 - b3c = 402, where a, b, c are digits.

Compute:

• (900 + 10a + 5) - (100b + 30 + c) = 402
• 905 + 10a - 100b - 30 - c = 402
• 875 + 10a - 100b - c = 402
• 10a - 100b - c = -473
• 100b + c = 473 + 10a

Since b ∈ {1,…,9} and c ∈ {0,…,9}, the right side 473 + 10a must be between 100 and 999. The feasible option is b = 5:

• 500 + c = 473 + 10a → c = 10a - 27 To have 0 ≤ c ≤ 9, a must be 3, giving c = 3.

Thus a = 3, b = 5, c = 3, and the equation is:

• 935 - 533 = 402

Answer: 935 - 533 = 402.