Question

Find the sum of all natural numbers lying between 100 and 1000 which are multiple of 5

Answer 1

Answer:

98450

Step-by-step explanation:

Between 100 and 1000

i.e our choices are from 105 to 995

we need to exclude 100 and 1000

Formulas

Sn = n/2 ( a + l )

l = a + ( n -1 )d

So, the first number which is a multiple of 5 is 105 that is a

and the last number which is a multiple of 5 is 995 that is l

Now, since l = 995

a + (n - 1)d = 995

Here, a = 105

d = 5

105 + (n -1)5 = 995

105 + 5n - 5 = 995

5n = 995 - 105 + 5

5n = 895

n = 179

Now,

Sn = n/2 ( a + l )

= 179/2 ( 105 + 995 )

= 179/2 ( 1100 )

= 196900/2

Sn = 98450

Answer 2

Answer:

refers to the attachment