Question

Sum of all nos between w 100 and 1000 which are divisible by 5

Answer 1

Answer:

Step-by-step explanation:

Numbers divisible by 5 from 100 to 1000 are 105,110,.............995

This sequence is an A.P.

Here , first term =a =105

common difference = 5.

We know , a_n = a+(n-1)d

             995 = 105+(n-1)5

     \Rightarrow \, \, 890 = (n-1)5

   \Rightarrow \, \, 178 = (n-1)

\Rightarrow \, \, n=178+1=179

 

S_n = \frac{n}{2}[2a+(n-1)d]

      = \frac{179}{2}[2(105)+(179-1)5]

    = \frac{179}{2}[2(105)+178(5)]

     = 179\times 550

    = 98450

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