【慶應算数】等比数列の和に気づけば一瞬

#KeioJuniorHighSchool #2026 #GeometricProgression #FractionCalculation #MathEntranceExam ■ Problem Keio Junior High School 2026 1 − ( 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 ) ■ Observation The denominators are all 2, 4, 8, 16, 32, and 64 In other words, It's a geometric progression of 1/2. ■ Sum of a Geometric Sequence 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 = (1/2) × (1 − (1/2)^6) ÷ (1 − 1/2) ■ Calculation (1/2)^6 = 1/64 Therefore Sum = (1/2) × (1 − 1/64) ÷ (1/2) = 1 − 1/64 = 63/64 ■ Original Equation 1 − 63/64 = 1/64 ■ Conclusion 1/64 ■ Advice for Viewers Reducing all fractions is difficult "Continuous division by 2" is a geometric sequence The answer can be predicted by looking at the denominator of the last term Typically Keio-style This problem emphasizes discovering the rule rather than mathematical ability. 🔗 Related Videos & Recommended Links [Junior High School Entrance Exam Math Calculation Problem Explanation Series] ▶    • 灘中入試問題 2005年度1日目｜素因数分解で分数の計算問題   [Junior High School Entrance Exam Integer Properties Practice Problems] ▶    • 【魔方陣の攻略法】真ん中の数の見つけ方！公務員試験＆中学受験の数的処理対策｜算数過去...   [Kaisei Junior High School Entrance Exam Questions & Past Exam Questions Explanation Series] ▶    • 【開成中学の算数】単位分数の和と整数問題を徹底解説！2010年度過去問に挑戦｜中学受験算数   [Nada Junior High School Entrance Exam Questions & Past Exam Questions Explanation Series] ▶    • 灘中入試問題 2005年度1日目｜素因数分解で分数の計算問題   📢 Request to Viewers If you found this video helpful, please let us know by "like" or "commenting"! You're also welcome to request other questions. 📌 About This Channel This channel offers fun ways to learn arithmetic and mathematics while steadily improving the skills needed for exams. We fully support everyone who wants to "improve their thinking skills" and "overcome their weaknesses"! 📩 Job Requests/Inquiries For interviews and job inquiries, please contact: 📧 [email protected] #JuniorHighSchoolEntranceExams #ExamMath #Math