At Jefferson Elementary School, the number of teachers and students (kindergarten through sixth grade) totals 510. The ratio of students to teachers is 16 to 1. Kindergarten students make up 1/5 of the student population and fifth and sixth graders account for 1/3 of the remainder. Students in first and second grades account for 1/4 of all the students. If there are an equal number of students in the third and fourth grades, then the number of students in third grade is how many greater or fewer than the number of students in kindergarten?

12 greater
17 fewer
28 fewer
36 fewer
44 fewer

The explanation in the CAT, was good. my question is what should one do, when facing this kind of question.
When I saw this question, I thought "there are to many calcs that can go wrong, and it will take me no shorter then 2 min to solve it. I rather guess and use the time to make sure the next 2 or 3 questions are correct"

what do you think?

kill that noise.

you need to be able to do arithmetic quickly. if you can't do the requisite arithmetic in two minutes, then either
(1) you are spending too much time deliberating on how to set it up (perhaps taking a full minute or so to figure out 16x + x = 510)
or
(2) your arithmetic is unacceptably slow.

if (2) is the case, then you need to practice doing arithmetic until you can do it quickly. that practice will be unbelievably boring and mind-numbing, but it's necessary. if you are a total calculator jockey, you need to re-learn all that cool stuff you learned in sixth grade.

I was also slow on doing arithmetic calculations on this problem. Are there any sources on the web that have practice problems I can do to speed up my performance.

Thanks

not sure where you're at. if you're in the u.s., you could always try the math section at your local public library. the best place to find computational problems like this one is in a pre-algebra book, since 'pre-algebra' focuses on all that computational stuff that you have to learn before you can use scary variables.

if you go this route, then the older the book the better; in the last twenty years, math textbooks have become more and more of a joke (at least in this country, anyway).

if you're in asia, then i know that india and singapore have math textbooks for relatively young kids with excellent computational problems.