Find the sum of natural numbers 1+ 2 + 3 + 4 + ..... + 18.

1.	Find the sum of natural numbers 1+ 2 + 3 + 4 + ..... + 18.
Answer» Let S be the required sum. Therefore, S = 1 + 2 + 3 + 4 + 5 + .................... + 18. Clearly, it is an Arithmetic Progression whose first term = 1, last term = 18 and number of terms = 18. Therefore, S = 18/2 (18+1), [Using the formula S = n/2 (a+1)] = 18/2 (19) = 9 X 19 = 171 Therefore, the sum of first 18 natural numbers is 171.

Answer»

Let S be the required sum.

Therefore, S = 1 + 2 + 3 + 4 + 5 + .................... + 18.

Clearly, it is an Arithmetic Progression whose first term = 1, last term = 18 and number of terms = 18.

Therefore, S = 18/2 (18+1), [Using the formula S = n/2 (a+1)]

= 18/2 (19)

= 9 X 19

= 171

Therefore, the sum of first 18 natural numbers is 171.

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Find the sum of natural numbers 1+ 2 + 3 + 4 + ..... + 18.

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