Chapter 8
Predicting What Comes Next: Exploring Sequences and Progressions
CBSE Class 9
Mathematics Solutions
Educart Mathematics class Class 9 NCERT Exemplar cover
Question:

Find the smallest value of nn such that the sum of the first nn natural numbers is greater than 1,000.

Answer: Verified

We need: 1+2+3++n>10001 + 2 + 3 + \dots + n > 1000

Using the sum formula:

1+2+3++n=n(n+1)21 + 2 + 3 + \dots + n = \frac{n(n+1)}{2}

n(n+1)2>1000\frac{n(n+1)}{2} > 1000

n(n+1)>2000n(n + 1) > 2000

Check nearby values:

44×45=198044 \times 45 = 1980

45×46=207045 \times 46 = 2070

So, 44×452=990\frac{44 \times 45}{2} = 990

45×462=1035\frac{45 \times 46}{2} = 1035

Hence, the smallest value of nn is 4545.

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