How to get a high GRE quant score - For average math or non-math test takers

[giddy]

Originally Posted by sleepy_sentinel

Zorillo wrote:

'For example, what is the probability that a number amongst the first 1000 positive integers is divisible by 8? Don’t start counting the multiples of 8! The figure of 1000 is a red herring. Use a little common sense. The numbers will be 8,16,24,32…So, 1 in every 8 numbers is a multiple of 8, even if you consider the first million integers. So Probability is 1/8 (Question from Power-Prep.)'

Hi Zorrillo, I hate to nit-pick, but that approach only works because 1000 is divisible by 8.If the number mentioned was 999 or 1001, the probability would NOT have been 1/8.In my experience, its always better to do probability problems ab initio.
Great post otherwise.Do keep up the good work.

Cheers

How would you go about in solving the probability problem if the number is 999 or 1001? Thanks.

[Zonky]

First of all Zorrillo your post is just awsome! i have been thinking how much time I would require for preparing ..... Adonis, i checked out your post as well.. itz great too!

[MonaD]

Really a great post Zorillo, wonderful writeup for people who are just starting.

[vvv134]

How would you go about in solving the probability problem if the number is 999 or 1001? Thanks.

if you divide thousand by 8,youll realise that there are 125 multiples of 8 from one to thousand inclusive.hence prob of getting a multiple of 8 125/1000=1/8.if the number is 1001,then prob of getting multiple of 8 is 125/1001(slightly lesser since you have one more number that cant be divisible by 8).similarly if the number is 999,the prob is 124/999.(now there are only 124 multiples).

[jess_john]

well inspiring post
thank you

[October Tester]

Originally Posted by zorrillo

Rule of 3:

A car travels 50 km in 30 mins. How many kms does it travel in 15 mins?

30 mins == 50 kms
15 mins == ?


Rule of 5:

3 machines print 25 pages in 40 secs. How many pages do 5 machines of the same type print in 20 secs?

3 machines == 40 sec == 25 pages
5 machines == 20 sec == ?

Easy. They are called so because of the number of terms involved; 3 and 5 resp.

3 machines x 40 seconds = 120 machine-seconds make 25 pages

120 machine-seconds / 5 machines = 24 seconds for 5 machines do 25 pgs

Ratio: 24 secs/ 25 pgs = 20 secs/ x pgs

25(20) = 24x
x = 20.83 ?

5 machines in 20 seconds make 20.83 pages? Is this correct? Please advise.

[e.cartman]

Hi OctoberTester, imo 20.83 is correct.