Question

Insert $3$ arithmetic means between $5$ and $21$

Find sum of those mean

Answer 1

Let we insert thre arithmetic means m,n,o between 5 and 21

so Resulting sequence 5, m, n, o, 21 formed an AP of 5 terms

$\therefore 21=5+(5-1)d$

$\to d=\frac{16}{4}$

$\therefore$m=a+d=5+4=9

n=a+2d=5+8=13

o=a+3d=5+12=17

hence the three arithmetic means are 9,13,17 respectively.