Find how many three digit natural numbers are divisible by 5.

List of three digit number divisible by 5 are

100, 105,110,115,……….. 995

Let us find how many such number are there?

From the above sequence, we know that

t_n = 995, a = 100

t₁ = 105, t₂ = 110

Thus, d = t₂ – t₁ = 110 – 105 = 5

Now, By using n^th term of an A.P. formula

t_n = a + (n – 1)d

we can find value of “n”

Thus, on substituting all the value in formula we get,

995 = 100 + (n – 1)× 5

⇒ 995 – 100 = (n – 1)× 5

⇒ 895 = (n – 1) × 5

⇒ n = 179 + 1 = 180