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`        The series of natural numbers is divided into groups as follows; (1), (2, 3), (4, 5, 6,), (7, 8, 9, 10) and so on. Find the sum of the numbers is the nth groups is ? PS Options are attached in the image file!Please solve the question and tell me the answer. `
11 months ago

1673 Points
```							in the nth group, the last number will be n(n+1)/2 [by observation that last numbers 1, 3, 6, 10,.... are actually the sum of first n numbers, which is equal to n(n+1)/2]now, number of terms in nth group is obviously nso by sum of an AP, taking first term as the last term, difference as – 1, and number of terms n, we haveSn= n/2*[2*n(n+1)/2+(n – 1)*( – 1)]=n*(n^2+1)/2
```
11 months ago
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### Course Features

• 101 Video Lectures
• Revision Notes
• Test paper with Video Solution
• Mind Map
• Study Planner
• NCERT Solutions
• Discussion Forum
• Previous Year Exam Questions