**9/13/2014
**The
4^{th}
term of an arithmetic series is 16 whereas the 13^{th}
term is 43. Find the 20^{th}
term.

**Scroll
down for the solution.**

**9/13/2014
**Solution.
Since
the 4

a_{13
}=
a_{4
}+
9*d*
→ 43 = 16 + 9*d*
→ *d*
= 3

We
need the 20^{th}
term, so that a_{20}
= a_{4
}+
16*d*
= 16 + 16·3
= 64