Question

find the sum of all numbers between 700 and 800 (both inclusive) which are not divisible by 10

Answer 1

Answer:

Given to find the sum of all number lying between the range 700-800 which are not divisible by 10

• So let us. form a AP

The first and second term is .....

701,702,703......

In this AP the first term is 701 and the common difference is 702-701=1

So the Total number of this AP is given by

.

=> 100-10×1✓ (°•° Out of this 100 number between this range the 10 multiple of 10 must be diducted so as to get those number which are not divisible by 10 ) ✓

=> 100-10

=>90

Now the sum of those number which are not divisible by 10 is given by

$sn = \frac{n}{2} (2a + (n - 1)d)$

Now let us find the sum ✓

$= > s90 = \frac{90}{2} (2 \times 701 + (90 - 1) \times 1)$

$= > s \: 90 = 45(701 \times 2 + 89 \times 1)$

$</strong><strong>=</strong><strong>></strong><strong>s \:</strong><strong> 90 = 45(1402 + 89) \\ \\ = > s \: 90 = 45 \times 1491 \\ \\ = > s \: 90 = 67095 \:$

There fore the sum of the number between this range which are not divisible by 10 is 67095 ✓