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Answer 1 · 2017-04-02T11:21:25

$500 .$ $500.$

Recall that Arithmetic Mean (AM) of $a_1,a_2,a_3,...,a_n$ is

$AM=(a_1+a_2+a_3+...+a_n)/n$

We are given the following set of nos. :

$5, 10, 15, 20, ..., 995.$

To find, how many these nos. are, we observe their patern :

$5(1), 5(2), 5(3), 5(4), ..., 5(199) rArr n=199.$

By the Formula for Sum of $n$ terms of Arith. Seq.,

we get,

$AM=(5+10+15+20+...+995)/199$

$={199/2(5+995)}-:199$

$:. AM=500.$

Enjoy Maths.!