Question

1 + 2 + 3 ......... + n = 55 What is the value of n?​

Answer 1

Answer:

10

Step-by-step explanation:

n(n+1)/2=55

n²+n-1=110

n²+n-1-110=0

n+11, n-10 (Factor)

n=-11

n=10

Answer 2

10

Given:

1 + 2 + 3 ......... + n = 55

To Find:

The value of n.

Solution:

WKT;

Sum of natural numbers 1 +2+3+4+5+..... = n(n+1)/2

It is given that 1+2+3+.....n = 55

Hence, n(n+1)/2 = 55

=> n(n+1) = 110

=> n^2 + n - 110 = 0

=> n^2 +11n - 10n -110 = 0

=> n(n+11) - 10(n+11) = 0

=> (n+11)(n-10) = 0

=> n = 10,-11

'n' cannot be negative.

Hence, the value of n = 10.

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