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Which number should be added to (S_{68}) to get (S_{75})?(S_{68}) में कौन सी संख्या जोड़ने पर (S_{75}) प्राप्त होगा?
Answer and explanationउत्तर और व्याख्या
Correct answer:सही उत्तर: 504504
Since \(S_{75}=S_{68}+(69+70+\cdots+75)\), the required number is the sum of the terms from 69 to 75. There are 7 terms, so their sum is \(\frac{7}{2}(69+75)=\frac{7}{2}\times144=504\). Hence, 504 is correct. Exam tip: When finding \(S_b-S_a\), add the terms from \(a+1\) to \(b\).क्योंकि \(S_{75}=S_{68}+(69+70+\cdots+75)\), इसलिए जोड़ी जाने वाली संख्या \(69\) से \(75\) तक के पदों का योग होगी। यहाँ 7 पद हैं, अतः योग \(\frac{7}{2}(69+75)=\frac{7}{2}\times144=504\) है। इसलिए सही उत्तर 504 है। परीक्षा टिप: \(S_b-S_a\) निकालते समय \(a+1\) से \(b\) तक के पद जोड़ें।
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