SBI PO Prelims practice question
Find the value of 1² + 2² + 3² + … + 9².
From a SBI PO Prelims Quantitative Aptitude practice set · Quantitative Aptitude
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Correct answer: (C) 285
Sum of the squares of the first n natural numbers: Σn² = n(n + 1)(2n + 1)/6. With n = 9: 9 × 10 × 19/6 = 1710/6 = 285. (Using [n(n + 1)/2]² here is the Σn³ formula, a common mix-up.)
हिंदी में प्रश्न
1² + 2² + 3² + … + 9² का मान ज्ञात कीजिए।
उत्तर जाँचने के लिए किसी विकल्प पर टैप करें।
उत्तर और व्याख्या देखें
सही उत्तर: (C) 285
प्रथम n प्राकृत संख्याओं के वर्गों का योग: Σn² = n(n + 1)(2n + 1)/6। n = 9 रखने पर: 9 × 10 × 19/6 = 1710/6 = 285। ([n(n + 1)/2]² लेना Σn³ का सूत्र है, यह सामान्य भ्रम है।)
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