[SOLVED] SAT math page 653

• September 28th 2008, 01:38 AM
fabxx
[SOLVED] SAT math page 653
8, 17, 26, 35, 44, ...

The first 5 terms in a sequence are shown above. Each term after the first is found by adding 9 to the term immediately preceding it. Which term in this sequence is equal to 8+(26-1)9?

a) the 8th
b) the 9th
c) the 25th
d) the 26th
e) the 27th

I picked the 27th since i remembered there was a formula that was (n-1). But the correct is d) the 26th. why? Instead of writing out all the terms is there another other way? A faster way? Thanks in advance!
• September 28th 2008, 01:41 AM
Moo
Quote:

Originally Posted by fabxx
8, 17, 26, 35, 44, ...

The first 5 terms in a sequence are shown above. Each term after the first is found by adding 9 to the term immediately preceding it. Which term in this sequence is equal to 8+(26-1)9?

a) the 8th
b) the 9th
c) the 25th
d) the 26th
e) the 27th

I picked the 27th since i remembered there was a formula that was (n-1). But the correct is d) the 26th. why? Instead of writing out all the terms is there another other way? A faster way? Thanks in advance!

It is almost correct :)

See how it is defined :

$a_{\color{red}n}=a_1+({\color{red}n}-1)r$

So if you're given $8+({\color{red}26}-1)9$, can you see what ${\color{red}n}$ is ?
• September 28th 2008, 01:47 AM
fabxx
Oh haha. Clumsy me. Thanks moo