Question

if 213 ,k,518 are in ap find the value of k​

Answer 1

$2k = 213 + 518 \\ \\ \: \: \: \: \: = 731 \\ \\ k = \frac{731}{2} \\ \\ \: \: \: = 365.5$

Answer 2

213 , k , 518 are in arithmetic progression.

we know, common difference of an arithmetic progression always remains same.

so, k - 213 = 518 - k

or, k + k = 518 + 213

or, 2k = 731

or, k = 365.5

hence, value of k = 365.5