If a(25) - a(20) = 45 for an arithmetic progression, what is the value of d?
If a1, a2, a3, ........a24 are in arithmetic progression and a1 + a5 + a10 + a15 + a20 + a24 = 225, then find the value of
a1 + a2 + a3 + ..........+ a23 + a24
If terms 9, x, 21 form an arithmetic progression, then the value of x is ____.