Question

1. What is the sum of numbers from 1 to 9 ?​

Answer 1

Answer:

45 is the correct Answer.......

Answer 2

Answer:

The sum of numbers from 1 to 9  = 45

Step-by-step explanation:

Given numbers are 1 to 9

Required to find the sum of the above number

Recall the formula

Sum of first n- natural numbers = $\frac{n(n+1)}{2}$

Solution:

Since the numbers from 1 to 9 are natural numbers, we can calculate the sum of numbers from 1 to 9 using the above formula

Hence the sum of numbers from 1 to 9 = $\frac{9X10}{2}$

= $\frac{90}{2}$

= 45

Sum of numbers from 1 to 9 = 45

It can also be calculated by taking the numbers 1 to 9 as AP and applying the sum to n-terms of AP

Sum to n terms of an AP = $s_n = \frac{n}{2} [2a+(n-1)d],$ where a is the first term and d is the common difference

Here a = 1

d = 1

n = 9

$s_9 = \frac{9}{2} [2X1+(9-1)X1],$

$s_9 = \frac{9}{2} [2+8],$

= $\frac{9}{2} X10$

= 45

$s_9 = 45$

∴ The sum of numbers from 1 to 9  = 45

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