Squence

by **Capthan** Sun Sep 28, 2008 7:55 am

240,120,60,30......
In the sequence above, each term after the first is 1/2 of the preceding term. What is the least term of the squence that is greater than 1?

A) 32/15
B) 16/15
C) 15/8
D) 15/4
E) 15/2
Please explain your answer.

by **Kunal** Sun Sep 28, 2008 9:55 am

The sequence will continue as follows...

240,120,60,30, 15, 15/2, 15/4, 15/8,

The next term cud be 15/16 but the denominator gets bigger than the numerator so 15/16 is less than 1. So 15/8 is the last # in sequence >1.

by **RonPurewal** Tue Oct 14, 2008 4:56 am

Kunal Wrote:The sequence will continue as follows...

240,120,60,30, 15, 15/2, 15/4, 15/8,

The next term cud be 15/16 but the denominator gets bigger than the numerator so 15/16 is less than 1. So 15/8 is the last # in sequence >1.

yep, this is about the best you can do.

in any case, two lessons:

1 * DO NOT DELIBERATE as to whether to try a particular method of solution - just do it.
many students will waste precious time just sitting there staring at this problem, wondering whether they should grind out the next few terms. just dig in and find the terms.

2 * try to develop enough number sense to be able to look at this and tell, right away, that you won't have to go through too many terms.
this doesn't mean that you need to know the exact number of terms at a glance, but it does mean that you should be able to differentiate between "oh, that's easy, i only have to grind out a few terms" and "omg, no way, i'll have to find hundreds of them".
practice + observation makes perfect.