From $n \equiv 5 \pmod{6}$, $n = 6k + 5$. Substitute into the first congruence: $6k + 5 \equiv 3 \pmod{7} \Rightarrow 6k \equiv -2 \pmod{7} \Rightarrow 6k \equiv 5 \pmod{7}$. Multiply both sides by the modular inverse of 6 mod 7 (which is 6, since $6 \times 6 = 36 \equiv 1 \pmod{7}$): $k \equiv 5 \times 6 \equiv 30 \equiv 2 \pmod{7}$. Thus, $k = 7m + 2$, and $n = 6(7m + 2) + 5 = 42m + 17$. The two-digit solutions are when $m = 0$: $n = 17$ and $m = 1$: $n = 59$. The smallest is $\boxed{17}$.

["Understanding Congruences: Solving $n \equiv 5 \pmod{6}$ and Its Implications for Modulo 7", "In number theory, modular arithmetic plays a central role in solving equations and understanding patterns in integers. One fascinating application involves solving simple linear congruences and using substitution to derive deeper relationships. Let’s explore a concrete problem involving the congruence $ n \equiv 5 \pmod{6} $, analyze its implications modulo 7, and ultimately determine the two-digit solutions.", "---", "### From the Congruence $ n \equiv 5 \pmod{6} $", "The expression $ n \equiv 5 \pmod{6} $ means that $ n $ leaves a remainder of 5 when divided by 6. This can be written algebraically as:\n[\nn = 6k + 5\n]\nfor some integer $ k $. This simple form enables us to substitute $ n $ into other congruences — especially modulo 7, a common prime modulus used in number theory.", "---", "### Substituting into a Modulo 7 Congruence", "Consider the congruence:\n[\n6k + 5 \equiv 3 \pmod{7}\n]\nSubtract 5 from both sides:\n[\n6k \equiv -2 \pmod{7}\n]\nSince $-2 \equiv 5 \pmod{7}$ (because $-2 + 7 = 5$), the equation becomes:\n[\n6k \equiv 5 \pmod{7}\n]", "---", "### Finding the Modular Inverse of 6 Modulo 7", "To solve for $ k $, we need the modular inverse of 6 modulo 7 — a number $ x $ such that:\n[\n6x \equiv 1 \pmod{7}\n]\nTesting small values:\n- $ 6 \ imes 1 = 6 \equiv 6 <br/>\not\equiv 1 $\n- $ 6 \ imes 2 = 12 \equiv 5 <br/>\not\equiv 1 $\n- $ 6 \ imes 6 = 36 \equiv 1 \pmod{7} $ (since $ 36 \div 7 = 5 $ remainder 1)", "Thus, the inverse of 6 mod 7 is 6. Multiply both sides of $ 6k \equiv 5 \pmod{7} $ by 6:\n[\nk \equiv 6 \ imes 5 = 30 \pmod{7}\n]\nNow compute $ 30 \mod 7 $:\n[\n30 \div 7 = 4 \ ext{ remainder } 2 \Rightarrow 30 \equiv 2 \pmod{7}\n]\nTherefore,\n[\nk \equiv 2 \pmod{7}\n]", "---", "### Reconstructing $ n $ Using the Value of $ k $", "Recall $ n = 6k + 5 $. Substitute $ k = 7m + 2 $ (since $ k \equiv 2 \pmod{7} $):\n[\nn = 6(7m + 2) + 5 = 42m + 12 + 5 = 42m + 17\n]", "This provides a general solution:\n[\nn = 42m + 17\n]", "---", "### Finding Two-Digit Solutions", "We seek two-digit values of $ n $, so:\n- For $ m = 0 $: $ n = 42(0) + 17 = 17 $\n- For $ m = 1 $: $ n = 42(1) + 17 = 59 $\n- For $ m = 2 $: $ n = 42 \ imes 2 + 17 = 84 + 17 = 101 $ (not a two-digit number)", "Thus, the valid two-digit solutions are $ n = 17 $ and $ n = 59 $. The smallest is\n[\n\boxed{17}\n]", "---", "### Why This Matters", "This method exemplifies a powerful technique in modular arithmetic:\n- Start with a congruence in one modulus\n- Substitute via algebraic expression\n- Use modular inverses to isolate variables\n- Derive a simpler form modulo another modulus", "Such reasoning is foundational in cryptography, coding theory, and algorithm design. Recognizing relationships between congruences allows efficient exploration of number patterns and efficient computation within finite rings.", "Whether you're solving for integers, optimizing algorithms, or studying cryptographic systems, mastering these substitution and reduction strategies is essential.", "---", "Keywords:\nmodular arithmetic, congruence equations, linear congruences, modular inverse, solving modulo 7, 6 mod 7, $ n \equiv 5 \pmod{6} $, two-digit solutions, $ k \equiv 2 \pmod{7} $, $ n = 42m + 17 $, number theory applications."]









